diff --git a/.changeset/lightbox-pause-on-close.md b/.changeset/lightbox-pause-on-close.md
new file mode 100644
index 0000000000000..c3f3f1866407d
--- /dev/null
+++ b/.changeset/lightbox-pause-on-close.md
@@ -0,0 +1,7 @@
+---
+'@astryxdesign/core': patch
+---
+
+[fix] Closing a Lightbox stops a video that was playing. The viewer stays mounted, so the picture and its sound would otherwise continue after Close, Escape, or a tap outside. A viewer that is already closed does not start playback either. Opening it again plays the current video when `hasAutoPlay` is set.
+
+@SebTardif
diff --git a/packages/core/src/Lightbox/Lightbox.test.tsx b/packages/core/src/Lightbox/Lightbox.test.tsx
index 937f28911e5e5..5f217cf6f0c3c 100644
--- a/packages/core/src/Lightbox/Lightbox.test.tsx
+++ b/packages/core/src/Lightbox/Lightbox.test.tsx
@@ -598,6 +598,103 @@ describe('Lightbox', () => {
       expect(pause).toHaveBeenCalledTimes(1);
     });
 
+    it('pauses a playing video when the viewer closes', () => {
+      const items = [
+        {src: '/clip.mp4', alt: 'A clip', type: 'video' as const},
+        {src: '/b.jpg', alt: 'Image B'},
+      ];
+      const view = (isOpen: boolean) => (
+        <Lightbox
+          isOpen={isOpen}
+          onOpenChange={() => {}}
+          media={items}
+          index={0}
+        />
+      );
+      const {rerender} = render(view(true));
+      const video = document.querySelector('video')!;
+      // Started by someone: playing, with its sound. Closing keeps the
+      // element mounted inside the closed dialog.
+      const pause = vi.fn();
+      video.pause = pause;
+      Object.defineProperty(video, 'paused', {
+        configurable: true,
+        get: () => pause.mock.calls.length > 0,
+      });
+      rerender(view(false));
+      expect(document.querySelector('video')).toBe(video);
+      expect(pause).toHaveBeenCalledTimes(1);
+    });
+
+    it('pauses a single playing video when the viewer closes', () => {
+      const media = {src: '/clip.mp4', alt: 'A clip', type: 'video' as const};
+      const view = (isOpen: boolean) => (
+        <Lightbox isOpen={isOpen} onOpenChange={() => {}} media={media} />
+      );
+      const {rerender} = render(view(true));
+      const video = document.querySelector('video')!;
+      const pause = vi.fn();
+      video.pause = pause;
+      Object.defineProperty(video, 'paused', {
+        configurable: true,
+        get: () => pause.mock.calls.length > 0,
+      });
+      rerender(view(false));
+      expect(document.querySelector('video')).toBe(video);
+      expect(pause).toHaveBeenCalledTimes(1);
+    });
+
+    it('plays a single video again when the viewer reopens, with hasAutoPlay', () => {
+      const play = vi
+        .spyOn(HTMLMediaElement.prototype, 'play')
+        .mockImplementation(async () => {});
+      try {
+        const media = {src: '/clip.mp4', alt: 'A clip', type: 'video' as const};
+        const view = (isOpen: boolean) => (
+          <Lightbox
+            isOpen={isOpen}
+            onOpenChange={() => {}}
+            media={media}
+            hasAutoPlay
+          />
+        );
+        const {rerender} = render(view(true));
+        expect(play).toHaveBeenCalledTimes(1);
+        const video = document.querySelector('video')!;
+        const pause = vi.fn();
+        video.pause = pause;
+        Object.defineProperty(video, 'paused', {
+          configurable: true,
+          get: () => pause.mock.calls.length > 0,
+        });
+        rerender(view(false));
+        expect(pause).toHaveBeenCalledTimes(1);
+        rerender(view(true));
+        expect(play).toHaveBeenCalledTimes(2);
+        expect(play.mock.contexts.at(-1)).toBe(video);
+      } finally {
+        play.mockRestore();
+      }
+    });
+
+    it('withholds autoplay while the viewer is mounted closed', () => {
+      const media = {src: '/clip.mp4', alt: 'A clip', type: 'video' as const};
+      const view = (isOpen: boolean) => (
+        <Lightbox
+          isOpen={isOpen}
+          onOpenChange={() => {}}
+          media={media}
+          hasAutoPlay
+        />
+      );
+      const {rerender} = render(view(false));
+      // The element stays mounted. The attribute would start playback once
+      // the file loads, after the close effect has already run.
+      expect(document.querySelector('video')).not.toHaveAttribute('autoplay');
+      rerender(view(true));
+      expect(document.querySelector('video')).toHaveAttribute('autoplay');
+    });
+
     it("keeps a paged-away video's element and time once the viewer pages back", () => {
       const items = [
         {src: '/clip.mp4', alt: 'A clip', type: 'video' as const},
diff --git a/packages/core/src/Lightbox/Lightbox.tsx b/packages/core/src/Lightbox/Lightbox.tsx
index a219aa915f650..485e340dbc463 100644
--- a/packages/core/src/Lightbox/Lightbox.tsx
+++ b/packages/core/src/Lightbox/Lightbox.tsx
@@ -623,11 +623,23 @@ export function Lightbox({
   // A video left on another page stops: the pager keeps the neighbours
   // mounted, and a playing one would go on, with its sound, off screen. With
   // `hasAutoPlay`, the video paged to plays again, as a newly shown one does.
+  // The closed dialog keeps them mounted too, so closing stops a playing
+  // video. A single video has no page element.
   useEffect(() => {
     const container = containerRef.current;
     if (container == null) {
       return;
     }
+    if (!isOpen) {
+      for (const video of container.querySelectorAll<HTMLVideoElement>(
+        'video',
+      )) {
+        if (!video.paused) {
+          video.pause();
+        }
+      }
+      return;
+    }
     for (const video of container.querySelectorAll<HTMLVideoElement>(
       '[data-lightbox-page]:not([data-current]) video',
     )) {
@@ -635,14 +647,17 @@ export function Lightbox({
         video.pause();
       }
     }
-    const current = container.querySelector<HTMLVideoElement>(
-      '[data-lightbox-page][data-current] video',
-    );
+    const onAPage = container.querySelector('[data-lightbox-page]') != null;
+    const current =
+      container.querySelector<HTMLVideoElement>(
+        '[data-lightbox-page][data-current] video',
+      ) ??
+      (onAPage ? null : container.querySelector<HTMLVideoElement>('video'));
     if (hasAutoPlay && current != null && current.paused) {
       // A browser can refuse playback without a user's gesture.
       void current.play()?.catch(() => {});
     }
-  }, [index, hasAutoPlay]);
+  }, [index, hasAutoPlay, isOpen]);
 
   // The backdrop, the controls and the pages a dismissal faded, to restore
   // exactly those. A page faded as a neighbour may be the current one when
@@ -1323,7 +1338,7 @@ export function Lightbox({
         src={src}
         aria-label={alt}
         controls
-        autoPlay={isCurrent && hasAutoPlay}
+        autoPlay={isOpen && isCurrent && hasAutoPlay}
         preload={isCurrent ? 'auto' : 'metadata'}
         {...stylex.props(styles.video)}
       />