In this study, 50 children between 3 and 12 years old with formally diagnosed autistic spectrum disorders (ASD) and also having significant mitochondrial dysfunction will be treated for a 3 month period with the Mitochondrial Cocktail, a combination of specific nutritional supplements and metabolite intermediates (including anti-oxidants) and bio-energy substrates. A series of neurological and psychological evaluations will be conducted by trained evaluators/clinicians to evaluate both the severity and the clinical presentation of the ASD/mitochondrial dysfunction with each subject at baseline prior to treatment, after the 3 month treatment and again at 6 months, after another 3 month non-treatment period. In addition, laboratory investigations will be conducted at the same time-points to assess the mitochondrial dysfunction and cellular biomarkers thought to be associated with autistic and mitochondrial disorders. These investigations will include the analysis of samples of blood and cheek/buccal swabs collected from each child to assess select biochemical markers of ASD. The Mitochondrial Cocktail treatment will be administered at home once a day continuously for a total of 3 months. All the children in the study will be treated with the same Mitochondrial Cocktail (an open label study).