1. This study presents the results of a 30-week double-blind, placebo-controlled trial exploring the effectiveness of ascorbic acid (8g/70kg/day) as a supplemental pharmacological treatment for autistic children in residential treatment. 2. Residential school children (N = 18) were randomly assigned to either ascorbate-ascorbate-placebo treatment order group or ascorbate-placebo-ascorbate treatment order group. Each treatment phase lasted 10 weeks and behaviors were rated weekly using the Ritvo-Freeman scale. 3. Significant group by phase interactions were found for total scores and also sensory motor scores indicating a reduction in symptom severity associated with the ascorbic acid treatment. 4. These results were consistent with a hypothesized dopaminergic mechanism of action of ascorbic acid.