From archival records, we assessed outcomes achieved by preschoolers with both severe mental retardation and autistic features: (a) an experimental group (n = 11), which received intensive behavioral treatment, and (b) a comparison group (n = 10), which received minimal treatment. At intake (mean CA = 3.08 years), the groups did not differ significantly on any variable. At follow-up children in the experimental group obtained a higher mean IQ and evinced more expressive speech than did those in the comparison group. Behavior problems diminished in both groups. Results indicate that intensively treated children achieved clinically meaningful gains relative to the comparison group but remained quite delayed.