A case of clinical porphyria cutanea tarda posed a diagnostic dilemma when screening tests for porphyrinuria gave negative results and two skin biopsy specimens failed to show the histologic picture of porphyria cutanea tarda, pseudoporphyria, or epidermolysis bullosa acquisita. The dilemma was resolved when the eruption cleared following elimination of naproxen from the patient's treatment. Subsequent naproxen challenge resulted in new bullae on the dorsum of the hands.