Pellagra defines systemic disease as resulting from a marked cellular deficiency of niacin. It is characterized by 4 "D's": diarrhea, dermatitis, dementia, and death. Diagnosis of pellagra is difficult in the absence of the skin lesions, and is often facilitated by the presence of characteristic ones. The dermatitis begins as an erythema. Acute pellagra resembles sunburn in its first stages, but tanning occurs more slowly than typically in sunburn. Exacerbation follows re-exposure to sunlight. In this work we review the findings of this once mysterious disorder, one that still challenges clinicians world-wide.