In a clinical trial, 20 children and adolescents with developmental disorders (age range 8 through 17 years) refractory to previous psychotropic treatments were administered the atypical neuroleptic risperidone (dose range 1.5 to 10 mg/day). In a follow-up period ranging from 8 to 15 months, risperidone demonstrated clinical efficacy in 13 children. Twelve patients were free of side effects and two had minor ones. Three patients had marked weight increase, and galactorrhea developed in two adolescent girls. In this open study, risperidone was associated with clinical improvement. However, controlled studies are needed to determine its relative efficacy and safety in this special population.