A 43-year-old man developed a skin eruption characterized by 'macules with blisters' typical to Stevens-Johnson syndrome, as well as erosions of the lips and buccal mucosa, 2 weeks after he had started treatment with lamotrigine. He had a fever (39.6 degrees C), elevated liver enzymes and atypical lymphocytes in the peripheral blood. This undoubtedly reflects a case of Stevens-Johnson syndrome induced by lamotrigine, but it can also fulfill the criteria of anticonvulsant hypersensitivity syndrome or drug rash with eosinophilia and systemic signs. A case that precisely fits the definition of two syndromes that have different characteristics, different treatments and different prognoses indicates that there is a flaw in the classification.