diff --git a/.changeset/quiet-trees-observe.md b/.changeset/quiet-trees-observe.md
new file mode 100644
index 000000000..6be9bacbe
--- /dev/null
+++ b/.changeset/quiet-trees-observe.md
@@ -0,0 +1,5 @@
+---
+"@solid-primitives/resize-observer": patch
+---
+
+Preserve hydration identifiers when `createElementSize` receives a target accessor during server rendering.
diff --git a/packages/resize-observer/src/index.ts b/packages/resize-observer/src/index.ts
index cddc6be22..7557c2c36 100644
--- a/packages/resize-observer/src/index.ts
+++ b/packages/resize-observer/src/index.ts
@@ -188,6 +188,9 @@ export function createElementSize(
   target: Accessor<Element | false | undefined | null> | Element,
 ): Readonly<NullableSize> {
   if (isServer) {
+    // Reserve the same hydration child id as the client-side target effect,
+    // without evaluating the accessor or touching browser APIs on the server.
+    if (typeof target === "function") createEffect(noop, noop);
     return ELEMENT_SIZE_FALLBACK;
   }
 
diff --git a/packages/resize-observer/test/hydration.test.tsx b/packages/resize-observer/test/hydration.test.tsx
new file mode 100644
index 000000000..a8aaf3c42
--- /dev/null
+++ b/packages/resize-observer/test/hydration.test.tsx
@@ -0,0 +1,71 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import {
+  renderHydrationRoundTrip,
+  type HydrationRoundTripResult,
+} from "../../../scripts/test-utils/hydration-harness.ts";
+
+describe("createElementSize hydration", () => {
+  let result: HydrationRoundTripResult | undefined;
+  const targets = new Set<Element>();
+  const disconnect = vi.fn(() => targets.clear());
+
+  beforeEach(() => {
+    targets.clear();
+    disconnect.mockClear();
+    vi.stubGlobal(
+      "ResizeObserver",
+      class {
+        observe(target: Element) {
+          targets.add(target);
+        }
+        unobserve(target: Element) {
+          targets.delete(target);
+        }
+        disconnect = disconnect;
+      },
+    );
+  });
+
+  afterEach(() => {
+    result?.cleanup();
+    result = undefined;
+    vi.unstubAllGlobals();
+  });
+
+  it.each(["accessor", "element"])(
+    "hydrates the %s target without replacing server nodes",
+    async path => {
+      result = await renderHydrationRoundTrip(
+        `
+import { createSignal } from "solid-js";
+import { isServer } from "@solidjs/web";
+import { createElementSize } from "@solid-primitives/resize-observer";
+
+export default function App() {
+  const [target, setTarget] = createSignal<HTMLDivElement>();
+  const size = createElementSize(${path === "accessor" ? "target" : 'isServer ? undefined as any : document.getElementById("measured")!'});
+  return <><div id="measured" ref={setTarget}>Width: </div><span>{size.width ?? "waiting"}</span><p>after size</p></>;
+}
+`,
+        import.meta.dirname,
+      );
+      expect(result.html).toContain("waiting");
+      expect(result.consoleMessages).toEqual([]);
+      expect(result.container.childNodes).toHaveLength(result.serverNodes.length);
+      result.serverNodes.forEach((node, index) => {
+        expect(result!.container.childNodes[index]).toBe(node);
+        expect(node.parentNode).toBe(result!.container);
+      });
+      expect(result.container.querySelectorAll("#measured")).toHaveLength(1);
+      expect(targets.size).toBe(1);
+      expect(targets.values().next().value).toBe(result.container.querySelector("#measured"));
+      expect(result.container.querySelector("p")?.textContent).toBe("after size");
+      if (path === "accessor")
+        expect(result.container.querySelector("span")?.textContent).toBe("0");
+      result.cleanup();
+      result = undefined;
+      expect(targets.size).toBe(0);
+      expect(disconnect).toHaveBeenCalledOnce();
+    },
+  );
+});
diff --git a/packages/resize-observer/test/index.test.ts b/packages/resize-observer/test/index.test.ts
index 7242d467c..ec52655b9 100644
--- a/packages/resize-observer/test/index.test.ts
+++ b/packages/resize-observer/test/index.test.ts
@@ -252,6 +252,37 @@ describe("createElementSize", () => {
   const div = document.createElement("div");
   div.__mock_size = { width: 100, height: 200, clientWidth: 90, clientHeight: 190 };
 
+  test("tracks replacement and missing targets and disconnects on disposal", () => {
+    _targets = new Set<Element>();
+    const next = document.createElement("div");
+    next.__mock_size = { width: 300, height: 400, clientWidth: 290, clientHeight: 390 };
+    const before = disconnect_count;
+    const { size, setTarget, dispose } = createRoot(dispose => {
+      const [target, setTarget] = createSignal<Element | null>(div);
+      return { size: createElementSize(target), setTarget, dispose };
+    });
+    flush();
+    expect(size).toEqual(div.__mock_size);
+    expect(_targets.size).toBe(1);
+    expect(_targets.values().next().value).toBe(div);
+    setTarget(next);
+    flush();
+    expect(size).toEqual(next.__mock_size);
+    expect(_targets.size).toBe(1);
+    expect(_targets.values().next().value).toBe(next);
+    setTarget(null);
+    flush();
+    expect(size).toEqual({ width: null, height: null, clientWidth: null, clientHeight: null });
+    expect(_targets.size).toBe(0);
+    setTarget(div);
+    flush();
+    expect(_targets.size).toBe(1);
+    expect(_targets.values().next().value).toBe(div);
+    dispose();
+    expect(_targets.size).toBe(0);
+    expect(disconnect_count).toBe(before + 1);
+  });
+
   test("will return element size immediately", () => {
     createRoot(dispose => {
       const { width, height, clientWidth, clientHeight } = createElementSize(div);
diff --git a/packages/resize-observer/test/server.test.ts b/packages/resize-observer/test/server.test.ts
index ebf6e11c3..1b8fc176c 100644
--- a/packages/resize-observer/test/server.test.ts
+++ b/packages/resize-observer/test/server.test.ts
@@ -1,5 +1,6 @@
 import { describe, test, expect, vi } from "vitest";
 import { createResizeObserver, createElementSize, createWindowSize } from "../src/index.js";
+import { renderToString } from "@solidjs/web";
 
 describe("server", () => {
   test("createResizeObserver", () => {
@@ -25,4 +26,36 @@ describe("server", () => {
     expect(size.width).toBe(0);
     expect(size.height).toBe(0);
   });
+
+  test("createElementSize does not read targets or construct observers during SSR", () => {
+    const observer = vi.fn(() => {
+      throw new Error("ResizeObserver must not be constructed on the server");
+    });
+    vi.stubGlobal("ResizeObserver", observer);
+    const accessor = vi.fn((): Element => {
+      throw new Error("The target accessor must not run on the server");
+    });
+    const element = {
+      getBoundingClientRect() {
+        throw new Error("The element must not be measured on the server");
+      },
+    } as unknown as Element;
+    try {
+      renderToString(() => {
+        for (const size of [createElementSize(accessor), createElementSize(element)]) {
+          expect(size).toEqual({
+            width: null,
+            height: null,
+            clientWidth: null,
+            clientHeight: null,
+          });
+        }
+        return "server-safe";
+      });
+      expect(accessor).not.toHaveBeenCalled();
+      expect(observer).not.toHaveBeenCalled();
+    } finally {
+      vi.unstubAllGlobals();
+    }
+  });
 });
diff --git a/scripts/test-utils/hydration-harness.ts b/scripts/test-utils/hydration-harness.ts
index 065bd530a..756edb377 100644
--- a/scripts/test-utils/hydration-harness.ts
+++ b/scripts/test-utils/hydration-harness.ts
@@ -130,6 +130,8 @@ export type HydrationRoundTripResult = {
   html: string;
   /** `container` element the server HTML was hydrated into — still attached to `document.body`. */
   container: HTMLElement;
+  /** Server-rendered top-level nodes, captured before hydration. */
+  serverNodes: Node[];
   /** Every `console.error`/`console.warn` message emitted while `hydrate()` ran. */
   consoleMessages: string[];
   /** Removes `container` from the document. Call in test cleanup. */
@@ -147,9 +149,11 @@ async function runHydrationRoundTrip(appSource: string, cwd: string): Promise<Hy
 
   const container = document.createElement("div");
   container.innerHTML = html;
+  const serverNodes = Array.from(container.childNodes);
   document.body.appendChild(container);
 
   const messages: string[] = [];
+  let dispose: (() => void) | undefined;
   const originalError = console.error;
   const originalWarn = console.warn;
   console.error = (...args: unknown[]) => {
@@ -166,7 +170,7 @@ async function runHydrationRoundTrip(appSource: string, cwd: string): Promise<Hy
     // HTML — jsdom doesn't run scripts assigned via .innerHTML, so this sets up the same global
     // hydrate() otherwise expects to already be there.
     (globalThis as any)._$HY = { events: [], completed: new WeakSet(), r: {}, fe() {} };
-    hydrate(() => App({}), container);
+    dispose = hydrate(() => App({}), container);
     // Solid finalizes hydration (drainHydrationCallbacks) via a `setTimeout`, after any
     // microtask-scheduled reactive updates have settled — wait for both ticks so a
     // late-firing hydration-mismatch warning isn't missed by the console restore below.
@@ -180,8 +184,12 @@ async function runHydrationRoundTrip(appSource: string, cwd: string): Promise<Hy
   return {
     html,
     container,
+    serverNodes,
     consoleMessages: messages,
-    cleanup: () => container.remove(),
+    cleanup: () => {
+      dispose?.();
+      container.remove();
+    },
   };
 }