A method is described for classifying and quantifying surface tissue damage caused by self-injurious behavior. The Self-Injury Trauma Scale permits differentiation of self-injurious behavior according to topography, location of the injury on the body, type of injury, number of injuries, and estimate of severity. Fifty pairs of independently scored records were subjected to interrater reliability analyses, and the following mean (median) percentage agreement scores were obtained: overall agreement, 97% (98%); location of injury, 99% (100%); type of injury, 96% (100%); number of injuries, 89% (100%); and severity of injury, 94% (100%). Percentage agreement also was calculated for three summary scores: Number Index, 90%; Severity Index, 92%; and Estimate of Current Risk, 100%. Potential applications and limitations of the scale are discussed.