The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- UFO tourism (1 member)
- UFOs and Sightings (0 members)
- Unexplained Phenomena (1 member)
- United Kingdom (1 member)
- United States of America (10 members)
- Urban Legend Reports (1 member)
- Urban Legends (1 member)
- Vault Administration (1 member)
- Vault Guidelines (1 member)
- Vault License Templates (6 members)
- Vault Maintenance (2 members)
- Vault Policies (2 members)
- Vault Templates (52 members)
- Vault chronology categories (2 members)
- Vault maintenance categories (1 member)
- Vermont (1 member)
- Waterloo, Ontario (1 member)
- West Yorkshire (1 member)
- Westminster (1 member)
- Witnesses (3 members)
- Writing Guidelines (1 member)
- Yvette Fielding (1 member)
- ✓ (82 members)