Background: Risperidone may be effective in improving tantrums, aggression, or self-injurious behaviour in children with autism, but often leads to weight gain. Method: Using a quantitative Food Frequency Questionnaire (FFQ), we prospectively examined the nutritional intake of 20 children with autism participating in a randomised placebo-controlled trial of risperidone for disruptive behaviours. Results: At baseline, the mean intakes for macronutrients, vitamins and minerals exceeded Dietary Reference Intakes (DRIs). However there was substantial inter-participant variability, with individual deficiencies ([less than]80% of DRI) in the intake of calcium (9 of 20 participants), pantothenic acid (6 of 20), vitamin D (5 of 20) and vitamin K (8 of 20). For the participants for whom FFQs were available, there was an increase in weight and an increase in vitamin K intake after 2 months of risperidone treatment (n=9) compared to placebo (n=8). An additional 4 months of risperidone treatment (n=8) did not result in significant changes in reported nutritional balance. Conclusion: These pilot data suggest that treatment with risperidone did not significantly affect the nutritional balance of this small group of children. (Contains 2 tables and 1 figure.)