| lse | Oracle Utilities Load Analysis Input |
| lsg | LimeSurvey Group Structure XML |
| lsi | SAP Business Objects Local Security Information File |
| lsim | LogicSim Circuit |
| lsl | LightScribe Label |
| lslibrary | LittleSnapper Library Package |
| lsn | MakeMusic Finale Lesson |
| lsopt | LS-OPT Data |
| lsq | PaleoMag Least Squares Data |
| lsr | LANsurveyor Report |
| lst | Adobe Font List |
| lst | E-Sword v8 Verse List |
| lstx | E-Sword v9 Verse List |
| lsu | LANsurveyor Map |
| lsw | DxLibraryStudio Workspace |
| lsz | Litestep Theme File |
| lt | Moltemplate Data File |
| lt2 | Poser Light Data |
| lta | Monolith LithTech Game Engine Data |
| ltc | Linguistic Tree Constructor Data |
| ltcx | Linguistic Tree Constructor XML Data |
| ltd | HPE Library and Tape Tools Support Ticket |
| ltd | LivingTime Data File |
| ltf | Frogans Short-cut |
| lth | Roxio Label Creator Style Data |
| lthmb | Adobe Presenter Audio Thumbnail |
| ltl | TwoTowers LTL Formula |
| ltn | Carlson Survey Lot Network File |
| ltt | HP Library and Tape Tools Log |
| ltz | Poser Compressed Light Data |
| ltz | Poser Light Data |
| lu | ThoughtWing Library Unit |
| luacodec | Reason Remote Lua Codec Data |
| luar | UltraDefrag Lua Report |
| lucidcolorset | Lucid Colorset Data |