Once a significant cause of morbidity and mortality, health care providers rarely see primary pellagra in developed countries where fortification of foods with niacin is commonplace and niacin-rich foods are generally widely available. We report a ten-year-old boy with autism spectrum disorder who presented with photosensitive dermatitis which resolved after vitamin supplementation and dietary changes. In this child, the pellagra developed as the result of a long-term pattern of selective eating. Restricted diets, even to the point of nutrient deficiencies, are well-documented among children with autism spectrum disorders (ASD).