To characterize injuries occurring in jails, we analyzed injury report forms from the New York City jail system. We abstracted data from 4695 injury report forms representing 3863 patients. Of the injuries reported, 66% were classified as intentional. The 2 leading causes of injuries were inmate-on-inmate aggression (40%) and slips and falls (27%). Injuries place a considerable burden on jail health care systems, and there is a need for more studies on this problem and development of injury prevention programs.