A man in his 20s presented with a one-day history of lesions on his right side, starting two hours after taking a metamizole tablet for a headache. He related a history of similar lesions, at exactly the same locations, a year before, after taking the same drug. On examination he presented well-demarcated erythematous patches, with violaceous bullous centres (figure 1). He had no fever or other systemic symptoms. No significant findings were present in the rest of the examination.