In the present study we confirm the previously reported high frequency of biochemical markers of mitochondrial dysfunction, namely hyperlactacidemia and increased lactate/pyruvate ratio, in a significant fraction of 210 autistic patients. We further examine the involvement of the mitochondrial aspartate/glutamate carrier gene ("SLC25A12") in mitochondrial dysfunction associated with autism. We found no evidence of association of the "SLC25A12" gene with lactate and lactate/pyruvate distributions or with autism in 241 nuclear families with one affected individual. We conclude that while mitochondrial dysfunction may be one of the most common medical conditions associated with autism, variation at the "SLC25A12" gene does not explain the high frequency of mitochondrial dysfunction markers and is not associated with autism in this sample of autistic patients.