diff --git a/src/utils/TaskManager.ts b/src/utils/TaskManager.ts
index 78f016d9..c7a04300 100644
--- a/src/utils/TaskManager.ts
+++ b/src/utils/TaskManager.ts
@@ -100,9 +100,12 @@ export class TaskManager extends Events {
 		} else {
 			// Fallback to legacy tag-based method with hierarchical support
 			if (!Array.isArray(frontmatter.tags)) return false;
-			return frontmatter.tags.some((tag: string) =>
-				typeof tag === 'string' && FilterUtils.matchesHierarchicalTagExact(tag, this.taskTag)
-			);
+			return frontmatter.tags.some((tag: string) => {
+				if (typeof tag !== 'string') return false;
+				// Obsidian metadata cache prepends '#' to frontmatter tags
+				const cleanTag = tag.startsWith('#') ? tag.slice(1) : tag;
+				return FilterUtils.matchesHierarchicalTagExact(cleanTag, this.taskTag);
+			});
 		}
 	}
 
diff --git a/tests/unit/utils/TaskManager.isTaskFile.test.ts b/tests/unit/utils/TaskManager.isTaskFile.test.ts
new file mode 100644
index 00000000..4c9aca3e
--- /dev/null
+++ b/tests/unit/utils/TaskManager.isTaskFile.test.ts
@@ -0,0 +1,206 @@
+/**
+ * TaskManager.isTaskFile - Tag hash prefix handling
+ *
+ * @see https://github.com/callumalpass/tasknotes/pull/1607
+ *
+ * Bug:
+ * Obsidian's metadata cache prepends '#' to frontmatter tags internally.
+ * For example, a file with `tags: [task]` in YAML frontmatter has
+ * `cache.frontmatter.tags` = `["#task"]` at runtime.
+ *
+ * TaskManager.isTaskFile() passed these raw cache values (with '#' prefix)
+ * to FilterUtils.matchesHierarchicalTagExact(), which compares them against
+ * the taskTag setting (e.g. "task" without '#'). The comparison "#task" !== "task"
+ * always failed, causing all tag-identified tasks to be invisible.
+ *
+ * Fix:
+ * Strip the '#' prefix from each tag before passing to matchesHierarchicalTagExact().
+ */
+
+import { describe, it, expect } from '@jest/globals';
+import { FilterUtils } from '../../../src/utils/FilterUtils';
+
+// Replicate the exact isTaskFile logic from TaskManager to test in isolation
+// without needing to construct the full TaskManager with App/Settings dependencies.
+interface IsTaskFileSettings {
+	taskIdentificationMethod: 'tag' | 'property';
+	taskTag: string;
+	taskPropertyName?: string;
+	taskPropertyValue?: string;
+}
+
+function isTaskFile(
+	frontmatter: Record<string, unknown> | null | undefined,
+	settings: IsTaskFileSettings
+): boolean {
+	if (!frontmatter) return false;
+
+	if (settings.taskIdentificationMethod === 'property') {
+		const propName = settings.taskPropertyName;
+		const propValue = settings.taskPropertyValue;
+		if (!propName || !propValue) return false;
+
+		const frontmatterValue = frontmatter[propName];
+		if (frontmatterValue === undefined) return false;
+
+		if (Array.isArray(frontmatterValue)) {
+			return frontmatterValue.some(
+				(val: unknown) => val === propValue
+			);
+		}
+		return frontmatterValue === propValue;
+	} else {
+		// Tag-based method (the fixed version)
+		if (!Array.isArray(frontmatter.tags)) return false;
+		return frontmatter.tags.some((tag: string) => {
+			if (typeof tag !== 'string') return false;
+			// Obsidian metadata cache prepends '#' to frontmatter tags
+			const cleanTag = tag.startsWith('#') ? tag.slice(1) : tag;
+			return FilterUtils.matchesHierarchicalTagExact(cleanTag, settings.taskTag);
+		});
+	}
+}
+
+describe('TaskManager.isTaskFile - tag hash prefix handling', () => {
+	const tagSettings: IsTaskFileSettings = {
+		taskIdentificationMethod: 'tag',
+		taskTag: 'task',
+	};
+
+	describe('Obsidian metadata cache tags (with # prefix)', () => {
+		it('should identify task when tags have # prefix from metadata cache', () => {
+			const frontmatter = { tags: ['#task', '#planning'] };
+			expect(isTaskFile(frontmatter, tagSettings)).toBe(true);
+		});
+
+		it('should identify task when only the task tag has # prefix', () => {
+			const frontmatter = { tags: ['#task'] };
+			expect(isTaskFile(frontmatter, tagSettings)).toBe(true);
+		});
+
+		it('should return false when # tags do not include the task tag', () => {
+			const frontmatter = { tags: ['#planning', '#work'] };
+			expect(isTaskFile(frontmatter, tagSettings)).toBe(false);
+		});
+	});
+
+	describe('Raw frontmatter tags (without # prefix)', () => {
+		it('should identify task with plain tag values', () => {
+			const frontmatter = { tags: ['task', 'planning'] };
+			expect(isTaskFile(frontmatter, tagSettings)).toBe(true);
+		});
+
+		it('should return false when plain tags do not include the task tag', () => {
+			const frontmatter = { tags: ['planning', 'work'] };
+			expect(isTaskFile(frontmatter, tagSettings)).toBe(false);
+		});
+	});
+
+	describe('Mixed tag formats', () => {
+		it('should handle mix of # prefixed and plain tags', () => {
+			const frontmatter = { tags: ['#planning', 'task'] };
+			expect(isTaskFile(frontmatter, tagSettings)).toBe(true);
+		});
+
+		it('should handle mix where task tag has # prefix among plain tags', () => {
+			const frontmatter = { tags: ['planning', '#task', 'work'] };
+			expect(isTaskFile(frontmatter, tagSettings)).toBe(true);
+		});
+	});
+
+	describe('Hierarchical tags with # prefix', () => {
+		it('should match hierarchical child tag with # prefix', () => {
+			const frontmatter = { tags: ['#task/project', '#planning'] };
+			expect(isTaskFile(frontmatter, tagSettings)).toBe(true);
+		});
+
+		it('should match hierarchical child tag without # prefix', () => {
+			const frontmatter = { tags: ['task/subtask', 'planning'] };
+			expect(isTaskFile(frontmatter, tagSettings)).toBe(true);
+		});
+
+		it('should not match when tag only starts with same characters', () => {
+			// "taskmaster" starts with "task" but is not "task" or "task/..."
+			const frontmatter = { tags: ['#taskmaster'] };
+			expect(isTaskFile(frontmatter, tagSettings)).toBe(false);
+		});
+	});
+
+	describe('Case insensitivity', () => {
+		it('should match case-insensitively with # prefix', () => {
+			const frontmatter = { tags: ['#Task', '#Planning'] };
+			expect(isTaskFile(frontmatter, tagSettings)).toBe(true);
+		});
+
+		it('should match case-insensitively without # prefix', () => {
+			const frontmatter = { tags: ['TASK'] };
+			expect(isTaskFile(frontmatter, tagSettings)).toBe(true);
+		});
+	});
+
+	describe('Edge cases', () => {
+		it('should return false for null frontmatter', () => {
+			expect(isTaskFile(null, tagSettings)).toBe(false);
+		});
+
+		it('should return false for undefined frontmatter', () => {
+			expect(isTaskFile(undefined, tagSettings)).toBe(false);
+		});
+
+		it('should return false when tags is not an array', () => {
+			const frontmatter = { tags: 'task' };
+			expect(isTaskFile(frontmatter, tagSettings)).toBe(false);
+		});
+
+		it('should return false for empty tags array', () => {
+			const frontmatter = { tags: [] };
+			expect(isTaskFile(frontmatter, tagSettings)).toBe(false);
+		});
+
+		it('should handle non-string values in tags array', () => {
+			const frontmatter = { tags: [42, null, '#task', undefined] };
+			expect(isTaskFile(frontmatter, tagSettings)).toBe(true);
+		});
+
+		it('should return false when all tag values are non-string', () => {
+			const frontmatter = { tags: [42, null, true, undefined] };
+			expect(isTaskFile(frontmatter, tagSettings)).toBe(false);
+		});
+
+		it('should not strip # from tags that are just "#"', () => {
+			const frontmatter = { tags: ['#'] };
+			expect(isTaskFile(frontmatter, tagSettings)).toBe(false);
+		});
+
+		it('should handle double-hash tags gracefully', () => {
+			// If somehow tags have "##task" (double hash), stripping one '#' yields "#task"
+			// which should NOT match "task"
+			const frontmatter = { tags: ['##task'] };
+			expect(isTaskFile(frontmatter, tagSettings)).toBe(false);
+		});
+	});
+
+	describe('Property-based identification (unaffected by fix)', () => {
+		const propSettings: IsTaskFileSettings = {
+			taskIdentificationMethod: 'property',
+			taskPropertyName: 'type',
+			taskPropertyValue: 'task',
+			taskTag: 'task',
+		};
+
+		it('should identify task by property value', () => {
+			const frontmatter = { type: 'task' };
+			expect(isTaskFile(frontmatter, propSettings)).toBe(true);
+		});
+
+		it('should return false when property does not match', () => {
+			const frontmatter = { type: 'note' };
+			expect(isTaskFile(frontmatter, propSettings)).toBe(false);
+		});
+
+		it('should handle array property values', () => {
+			const frontmatter = { type: ['note', 'task'] };
+			expect(isTaskFile(frontmatter, propSettings)).toBe(true);
+		});
+	});
+});