Psychiatric hospitalization of children with autism spectrum disorder and/or intellectual disability is common, however, the effectiveness of this intervention is largely unknown. Thirty-eight clinically-referred children 8–19 years old admitted to a specialized inpatient psychiatry unit were assessed by a consistent caregiver on the Aberrant Behavior Checklist-Irritability (ABC-I) subscale at admission, discharge and 2 months post discharge. There was a decrease in the mean ABC-I score from admission (27.3, SD 7.4) to discharge (11.9, SD 8.8), which was sustained at 2 months post discharge (14.8, SD 9.3) (p < 0.001). Seventy-eight percent of the subjects were rated as “Improved” on the clinician Clinical Global Impressions Improvement scale at discharge. The study is limited by lack of a control group, but offers preliminary evidence for specialized inpatient psychiatry as an intervention for serious behavioral disturbance in this population.