We evaluated an inexpensive, efficient, and noninvasive technique for measuring tissue damage produced by self-injurious behavior (SIB). The technique involved computerized measurement of wound surface area (WSA) based on digital photographs. In Study 1, we compared photographic measurement to a more commonly used procedure, transparency measurement, in estimating WSA of 20 wound models. Results showed that both methods were reliable and that there was a high degree of correspondence between the 2 sets of measures. In Study 2, we compared photographic WSA measures to direct-observation measures in documenting changes over time in the SIB exhibited by a woman with Prader-Willi syndrome. Results showed that increases and decreases in observed SIB during baseline and treatment conditions corresponded with changes in WSA measures, indicating that the computer-assisted photographic technique may be useful as a corroborative measure or as a primary measure when direct observation of SIB is not feasible. (Contains 6 figures.)