A 48-year-old woman presented to the general medicine clinic with a 6-month history of a worsening rash on her neck and arms. She also reported having diarrhea, fatigue, and loss of appetite, with an 8-kg weight loss over the same period; she had no neurologic symptoms. The patient lived in rural India, adhered to a vegetarian diet, and did not use alcohol. On physical examination, there were well-demarcated areas of hyperpigmentation on the sun-exposed areas of her neck and anterior chest (Panel A) and forearms (Panel B), with skin fissures in the antecubital fossa. Serum niacin testing was unavailable. A diagnosis of pellagra, or niacin deficiency, was made on the basis of the patient’s syndrome of diarrhea and symmetric, photosensitive dermatitis, including a typical Casal’s necklace rash. Pellagra that is caused by dietary deficiency persists in resource-limited countries, whereas it is associated more with alcohol use, bariatric surgery, or malabsorptive conditions in resource-rich countries. After the patient was treated with intravenous vitamin B complex followed by oral supplementation, the diarrhea resolved and the skin hyperpigmentation was reduced at follow-up 4 weeks later (Panels C and D).