diff --git a/frontend/src/routes/SearchFilterBar.svelte b/frontend/src/routes/SearchFilterBar.svelte
index 9ad11f39..344d6f26 100644
--- a/frontend/src/routes/SearchFilterBar.svelte
+++ b/frontend/src/routes/SearchFilterBar.svelte
@@ -15,6 +15,7 @@ let {
 	tagNames = $bindable<{ name: string; id?: string; color?: string; parentId?: string }[]>([]),
 	tagQ = $bindable(''),
 	tagOperator = $bindable<'AND' | 'OR'>('AND'),
+	undated = $bindable(false),
 	sort = $bindable('DATE'),
 	dir = $bindable('desc'),
 	showAdvanced = $bindable(false),
@@ -35,6 +36,7 @@ let {
 	tagNames?: { name: string; id?: string; color?: string; parentId?: string }[];
 	tagQ?: string;
 	tagOperator?: 'AND' | 'OR';
+	undated?: boolean;
 	sort?: string;
 	dir?: string;
 	showAdvanced?: boolean;
@@ -248,6 +250,33 @@ $effect(() => {
 					/>
 				</div>
 			</div>
+
+			<!-- Undated-only triage toggle (#668). aria-pressed states the toggle, not a
+			     colour; min-h-[44px] meets the senior-audience touch target (WCAG 2.5.5). -->
+			<div class="md:col-span-12">
+				<button
+					type="button"
+					data-testid="undated-only-toggle"
+					aria-pressed={undated}
+					onclick={() => {
+						undated = !undated;
+						(onSearchImmediate ?? onSearch)();
+					}}
+					class="inline-flex min-h-[44px] items-center gap-2 rounded border px-3 text-xs font-bold tracking-widest uppercase transition-colors {undated
+						? 'border-primary bg-primary text-primary-fg'
+						: 'border-line bg-muted text-ink-2 hover:bg-line'}"
+				>
+					<span
+						aria-hidden="true"
+						class="inline-flex h-4 w-4 items-center justify-center rounded-sm border {undated
+							? 'border-primary-fg bg-primary-fg/20'
+							: 'border-ink-3'}"
+					>
+						{#if undated}✓{/if}
+					</span>
+					{m.docs_filter_undated_only()}
+				</button>
+			</div>
 		</div>
 	{/if}
 </div>
diff --git a/frontend/src/routes/SearchFilterBar.svelte.spec.ts b/frontend/src/routes/SearchFilterBar.svelte.spec.ts
index 26d1d333..11f4c32d 100644
--- a/frontend/src/routes/SearchFilterBar.svelte.spec.ts
+++ b/frontend/src/routes/SearchFilterBar.svelte.spec.ts
@@ -128,6 +128,42 @@ describe('SearchFilterBar – AND/OR tag operator toggle', () => {
 	});
 });
 
+describe('SearchFilterBar – undated-only toggle (#668)', () => {
+	async function openAdvanced() {
+		const filterBtn = page.getByRole('button', { name: 'Filter', exact: true });
+		await filterBtn.click();
+	}
+
+	it('renders the "Nur undatierte" toggle in the advanced row', async () => {
+		render(SearchFilterBar, { ...defaultProps, sort: 'DATE', dir: 'desc' });
+		await openAdvanced();
+		await expect.element(page.getByTestId('undated-only-toggle')).toBeInTheDocument();
+	});
+
+	it('reflects the active undated state via aria-pressed', async () => {
+		render(SearchFilterBar, { ...defaultProps, sort: 'DATE', dir: 'desc', undated: true });
+		await openAdvanced();
+		await expect
+			.element(page.getByTestId('undated-only-toggle'))
+			.toHaveAttribute('aria-pressed', 'true');
+	});
+
+	it('calls onSearchImmediate when the undated toggle is clicked', async () => {
+		const onSearch = vi.fn();
+		const onSearchImmediate = vi.fn();
+		render(SearchFilterBar, {
+			...defaultProps,
+			onSearch,
+			onSearchImmediate,
+			sort: 'DATE',
+			dir: 'desc'
+		});
+		await openAdvanced();
+		await page.getByTestId('undated-only-toggle').click();
+		await expect.poll(() => onSearchImmediate.mock.calls.length).toBeGreaterThan(0);
+	});
+});
+
 describe('SearchFilterBar – tagQ live filter', () => {
 	it('calls onSearch when tag text changes in TagInput', async () => {
 		vi.stubGlobal(
diff --git a/frontend/src/routes/documents/+page.svelte b/frontend/src/routes/documents/+page.svelte
index f938334a..eabfea8c 100644
--- a/frontend/src/routes/documents/+page.svelte
+++ b/frontend/src/routes/documents/+page.svelte
@@ -32,10 +32,16 @@ let sort = $state(untrack(() => data.sort || 'DATE'));
 let dir = $state(untrack(() => data.dir || 'desc'));
 let tagQ = $state(untrack(() => data.tagQ || ''));
 let tagOperator = $state<'AND' | 'OR'>(untrack(() => (data.tagOp as 'AND' | 'OR') || 'AND'));
+let undated = $state(untrack(() => data.undated ?? false));
 
 function hasAdvancedFilters() {
 	return (
-		(data.tags?.length ?? 0) > 0 || !!data.senderId || !!data.receiverId || !!data.from || !!data.to
+		(data.tags?.length ?? 0) > 0 ||
+		!!data.senderId ||
+		!!data.receiverId ||
+		!!data.from ||
+		!!data.to ||
+		!!data.undated
 	);
 }
 
@@ -54,6 +60,7 @@ type FilterSnapshot = {
 	dir: string;
 	tagQ: string;
 	tagOp: 'AND' | 'OR';
+	undated: boolean;
 	zoomFrom?: string | null;
 	zoomTo?: string | null;
 };
@@ -77,6 +84,7 @@ function buildSearchParams(filters: FilterSnapshot, targetPage?: number): Svelte
 	if (filters.dir) params.set('dir', filters.dir);
 	if (filters.tagQ) params.set('tagQ', filters.tagQ);
 	if (filters.tagOp === 'OR') params.set('tagOp', 'OR');
+	if (filters.undated) params.set('undated', 'true');
 	if (filters.zoomFrom) params.set('zoomFrom', filters.zoomFrom);
 	if (filters.zoomTo) params.set('zoomTo', filters.zoomTo);
 	if (targetPage !== undefined && targetPage > 0) params.set('page', String(targetPage));
@@ -112,6 +120,7 @@ function navigateWithZoom(zoomFrom: string | null, zoomTo: string | null) {
 		dir,
 		tagQ,
 		tagOp: tagOperator,
+		undated,
 		zoomFrom,
 		zoomTo
 	});
@@ -136,7 +145,8 @@ function buildPageHref(targetPage: number): string {
 			sort: data.sort || '',
 			dir: data.dir || '',
 			tagQ: data.tagQ || '',
-			tagOp: (data.tagOp as 'AND' | 'OR') || 'AND'
+			tagOp: (data.tagOp as 'AND' | 'OR') || 'AND',
+			undated: data.undated ?? false
 		},
 		targetPage
 	);
@@ -188,7 +198,8 @@ async function editAllMatching() {
 			sort: '',
 			dir: '',
 			tagQ: data.tagQ || '',
-			tagOp: (data.tagOp as 'AND' | 'OR') || 'AND'
+			tagOp: (data.tagOp as 'AND' | 'OR') || 'AND',
+			undated: data.undated ?? false
 		});
 		params.delete('sort');
 		params.delete('dir');
@@ -226,6 +237,7 @@ $effect(() => {
 	dir = data.dir || 'desc';
 	tagQ = data.tagQ || '';
 	tagOperator = (data.tagOp as 'AND' | 'OR') || 'AND';
+	undated = data.undated ?? false;
 	if (hasAdvancedFilters()) showAdvanced = true;
 });
 </script>
@@ -255,6 +267,7 @@ $effect(() => {
 		bind:dir={dir}
 		bind:tagQ={tagQ}
 		bind:tagOperator={tagOperator}
+		bind:undated={undated}
 		initialSenderName={initialSenderName}
 		initialReceiverName={initialReceiverName}
 		navKey={navKey}