Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are infrequent mucocutaneous diseases, rapidly progressive and life-threatening. The clinical aspects and the management of TEN are exposed following a case.A man in his 40s presented to the emergency department with severe odynophagia, poor general condition and fever. His medical history was significant for HIV stage AIDS, and the treatment was discontinued 5 years before the present diagnosis. He was admitted for cerebral toxoplasmosis and discharged the previous 14 days with sulfadiazine. Erythematous-bullous lesions in the oral cavity, diffuse erythematous maculopapular rashes over his neck and chest, acute bilateral conjunctivitis and purulent urethritis was observed. The diagnostic suspicion was SJS/TEN due to sulfadiazine in immunosuppressed patients.This entity is infrequent but is a life-threatening dermatological emergency that requires immediate medical attention. Its diagnosis is mainly clinical, with a new drug history, prodromal symptoms and characteristic cutaneous–mucous lesions. Early diagnosis and rapid withdrawal of the drug improve the prognosis.