A literature search identified 17 articles reporting data on 34 subjects who engaged in precursors to severe problem behavior, which we examined to identify topographical and functional characteristics. Unintelligible vocalization was the most common precursor to aggression (27%) and property destruction (29%), whereas self- or nondirected movement was the most common precursor to SIB (32%). Unintelligible vocalization and object-directed movement were the most common precursors to behavior maintained by social-positive reinforcement (27% each), and unintelligible vocalization was the most common precursor to behavior maintained by social-negative reinforcement (29%). Only one precursor was reported for behavior maintained by automatic reinforcement. (Contains 1 table and 2 figures.)