A 53-year-old woman was seen for arthralgias, fever, and a painful rash developing at the end of a 7-day course of nitrofurantoin for a urinary tract infection. Her only other medication was naproxen, which was started after the onset of symptoms. Initial biopsy showed microscopic changes suggestive of a toxic eruption, but within 3 days the clinical signs and symptoms typical of Sweet's syndrome evolved. A repeat biopsy showed microscopic features characteristic of that diagnosis. The patient subsequently cleared with prednisone therapy. We report this patient as a case consistent with drug-induced Sweet's syndrome induced by nitrofurantoin.