The extent, nature, and treatment of self-injurious behavior was surveyed among 2,663 developmentally disabled children and adolescents in a large metropolitan school district during the 1984-85 school year. Sixty-nine, or 2.6 percent, of the students exhibited at least one type of self-injurious behavior during the preceding 12 months; 59 percent of these students were males and 41 percent were females. Most of the self-injurious students were either severely or profoundly retarded, and their mean age was 10.2 years. Although almost three-quarters of the students exhibited self-injurious behavior at least daily, only a third were engaged in formal treatment programs for the problem. More than half (53.6 percent) had been restrained during the preceding 12 months for such behavior, and 8.7 percent had received psychotropic medications. The authors believe that the development of effective treatment strategies for self-injurious individuals living in the community may help them avoid institutionalization.