Dapsone is used in prophylaxis for and treatment of Pneumocystis carinii pneumonia. We present a case of Stevens-Johnson syndrome that was likely induced by administration of dapsone. A review of charts at the HIV Treatment Center of Northwestern University (Chicago) revealed that 40.3% of patients treated with trimethoprim-sulfamethoxazole could not tolerate the medication, while 25.2% of those treated with dapsone were intolerant of the drug. We also found a higher rate of adverse reactions to dapsone among patients with prior intolerance to trimethoprim-sulfamethoxazole than among patients without such a history; however, the difference was not significant.