This study retrospectively examined the efficacy of a gluten-free and casein-free (GFCF) diet intervention as a means to improve verbal/nonverbal communication in children with autism spectrum disorders. Data were analyzed retrospectively from a randomized, double-blind, repeated measures crossover design study that included 13 children aged 2-16 years with autism spectrum disorders. Video recordings of at-home parent-child play were analyzed. Recordings were made at baseline, after 6 weeks on one of the diets (GFCF or regular diet), and after 6 weeks on the alternate diet. Findings of the current study indicated no statistically significant differences in verbal and nonverbal communication outcomes between GFCF and regular diet conditions. While results of this study demonstrate that double-blind clinical trials of diet intervention are feasible, they are inconclusive regarding the efficacy of diet for improving communication, perhaps due to the relatively short period of diet intervention used. Directions for future research are discussed as well as implications for clinical practice.