A modified functional analysis was used to assess the behavioral function of a profoundly retarded man's self-injurious behavior (SIB). Results of that analysis showed that the behavior was most likely to occur in a demand context (self-care instructions) but was maintained by positive reinforcement in the form of attention and physical contact. The results of the functional analysis also prescribed a treatment involving differential reinforcement of alternative behavior (DRA). Further investigation showed that other aberrant behaviors, such as aggression and disruption, were members of the same functional response class as SIB. The differential reinforcement of alternative behavior (DRA) procedure effectively reduced those behaviors while compliance to a self-care acquisition task increased markedly. The results are discussed in terms of the importance of determining behavioral function prior to treatment.