Abstract: A fast routine for testing whether a triangle and a box are overlapping in three dimensions is presented. The test is derived using the separating axis theorem, whereafter the test is simplified and the code is optimized for speed. We show that this approach is 2.3 vs. 3.8 (PC vs. Sun) times faster than previous routines. It can be used for faster collision detection and faster voxelization in interactive ray tracers. The code is available online.