LEGO[C] building materials have been adapted as a therapeutic modality for increasing motivation to participate in social skills intervention, and providing a medium through which children with social and communication handicaps can effectively interact. A 3 year retrospective study of long-term outcome for autistic spectrum children participating in LEGO[C] therapy (N = 60) compared Vineland Adaptive Behavior Scale socialization domain (VABS-SD) and Gilliam Autism Rating Scale social interaction subscale (GARS-SI) scores pre- and post-treatment with a matched comparison sample (N = 57) who received comparable non-LEGO[C] therapy. Although both groups made significant gains on the two outcome measures, LEGO[C] participants improved significantly more than the comparison subjects. Diagnosis and pre-treatment full-scale IQ scores did not predict outcome scores; however, Vineland adaptive behavior composite, Vineland communication domain, and verbal IQ all predicted outcome on the VABS-SD, especially for the LEGO[C] therapy group. Results are discussed in terms of implications for methods of social skills intervention for autistic spectrum disorders. (Contains 6 tables.)