A case report of cross-reactivity between phenytoin and carbamazepine, a 63-year-old male patient was prescribed phenytoin for generalized seizures and on the 15 th day of therapy developed generalized maculopapular eruptions. Phenytoin was discontinued, and carbamazepine was administered. After 28 days, he developed fever, generalized rashes with ulcers in the oral cavity. Carbamazepine was withdrawn, and the patient was treated symptomatically.