A 34-year-old man from Djibouti presented with a 14-year history of relapsing and remitting transverse white bands on the fingernails with sparing of the toenails. Examination revealed several transverse, white bands following the contour of the lunula on seven of his fingernails that did not fade upon compression of the digits (Figure). There was no onycholysis. No other skin lesions were noted. The patient reported having lived for 4 years (2000-2004) in a house that had well water as its primary water supply. This 4-year period was a stressful point in our patient's life. During that time, he had been a student at university. He had had no reported occupational exposure to arsenic. He reported being a cigarette smoker since 1996 but denied any illicit drug use or alcohol consumption. His past medical history was significant for hepatitis A infection, but he denied any history of systemic illness, including renal disease, heart disease, and lung disease. He denied any family history of leukonychia. He denied any trauma or participation in activities that require excessive use of his hands, and also denied manipulation of the cuticles. The patient's liver function tests, lipid panel, complete blood count, and urinalysis were all within normal limits. A blood test revealed normal arsenic levels. Histologic examination of the nail plate showed segmental parakeratosis, with no evidence of fungal organisms upon PAS staining.