Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are two of the most severe, rare, and life-threatening adverse reactions to medications. Their incidence is approximately two patients per million population per year. Several cases have been reported in the literature in which SJS and TEN have occurred in patients with a neoplasm undergoing radiation therapy and who are taking an anticonvulsant. We report a case of SJS-TEN that developed in a 51-year-old woman with nonresectable non-small-cell lung cancer during treatment with phenobarbital plus radiation therapy for bone metastases but in whom the irradiated areas did not exhibit the SJS skin reaction. To our knowledge, no similar cases have been reported in the literature.