This article reviews the diagnostic rationale for treatment of behavior disorders with psychotropic medication. After reviewing the concerns over the use of psychotropic medication and the use of diagnostic criteria with persons with developmental disabilities in the past, the variety of potential diagnoses that may underlie a behavior disorder are reviewed. A model to guide clinical decision making is then developed on the basis of this review, and areas for future research are suggested. The key questions are identified as making reliable differential diagnoses of behavior disorders and demonstrating that these differential diagnoses successfully identify more effective psychotropic medications for the treatment of behavior disorders in persons with developmental disabilities.