The occurrence of acute generalized exanthematous pustulosis adverse reactions to medication administration is becoming more frequent. This article reports the case of a 78-year-old woman who attended the clinic with generalized papules and pustules on the scalp, trunk and limbs, with a concordant histology study and who was diagnosed with acute generalized exanthematous pustulosis (AGEP) associated with the use of phenytoin, a medication that may cause different skin reactions and that has been previously related to this disease. The patient was treated with systemic steroids and the disease had a satisfactory outcome.