Autism is a complex neurodevelopmental disorder that is thought to involve an interaction between multiple and variable susceptibility genes (Keller & Persico, 2003), epigenetic effects (Beaudet, 2002), and environmental factors (London, 2000). The increase in the prevalence of autistic spectrum disorders from 4-5/10,000 in the 1980s to 30-60/10,000 in the last decade has raised great concern (Bertrand et al., 2001; DeStefano et al., 2004; Steinhausen et al., 1986; Yeargin-Allsopp et al., 2003). Research into potential therapeutic interventions designed to ameliorate the metabolic and clinical symptoms of autism is urgently needed to reduce the enormous public health burden of this disorder and to improve the quality of life for affected children and their families. Nutritional supplementation through subcutaneous injections of methyl B12 is a current treatment for children with autism that has anecdotal reports of remarkable clinical improvements and few side effects. However there are no published studies to support its clinical benefit.