A 25-year-old man presented with a 13-year history of an erythematous, papular eruption of his face and trunk, which was treated in the past as acne and psoriasis with isotretinoin and methotrexate, respectively. Histopathologic examination demonstrated an infiltrate of Langerhans cells, which was consistent with Langerhans cell histiocytosis. The epidemiology, clinical presentation, and treatment options of this disease are reviewed.