Dietary vitamin B12 deficiency was identified as a cause of partially reversible optic neuropathy in 3 autistic children. All of the affected children presented with gradual visual loss. Examination revealed optic atrophy, and further questioning regarding diet revealed that all 3 children had severe food selectivity and highly stereotyped diets that resulted in an almost total lack of animal products in their diets. Vitamin B12 levels were low in all 3 children. Treatment with intramuscular vitamin B12 and normalization of vitamin B12 levels resulted in improvement of visual functioning in all 3 children. These cases illustrate that food selectivity, a known complication of autism, can result in vitamin deficiency that can cause visual loss and optic atrophy. Physicians must have a high index of suspicion when evaluating children with autism and visual loss to detect this rare cause of optic atrophy.