| uu | Uuencoded Data |
| uue | Uuencoded Data |
| uuid | Linux UUID Data |
| uum | Minuum Keyboard Backup |
| uus | Ultra Utility Skin Data |
| uva | BRE U-value Calculator Data |
| uvf | Netica Uncertain Value Format File |
| uvl | µVision Signal Definition |
| uvla | µVision Signal Data |
| uvnts | UVScreenCamera Notes Data |
| uvr | 3DXML UVR Mesh Data |
| uvs | UVScreenCamera Segments Data |
| uvseg | UVScreenCamera Segments Data |
| uvt | DECE TTML Data |
| uvtsk | µVision Recorded Task-switching Data |
| uvtt | DECE TTML Data |
| uvutt | DECE TTML Data |
| uvw | Autodesk 3D Studio MAX UVW Coordinates |
| uvz | DECE ZIP Compressed Data |
| uwl | Novell GroupWise Custom Dictionary |
| uxd | Bruker RAW Data |
| uxd | URLBase URL Database |
| uxp | IGOR Pro Unpacked Experiment File |
| uxt | IGOR Pro Unpacked Experiment Template File |
| uyl | User Screen Editor Dictionary Data |
| uz1 | JB BAHN Scenery Archive |
| uz2 | JB BAHN Scenery Archive |
| uz4 | JB BAHN Scenery Archive |
| uzg | JB BAHN Scenery Archive |
| uzr | iModeller 3D UZR Model |
| v | Vivid 2.0 Input File |
| v00 | Kretz 3D Ultrasound Image |
| v01 | Genesis 2000 Data |
| v11 | ESR v11 Data |
| v16 | BrainVoyager QX MRI 16bit Data |