INTRODUCTION-The aim of this case report is to present a 15-year follow-up of a patient with phenytoin (PHT) intoxication with unilateral gingival hyperplasia (GH). MATERIAL AND METHODS-A 50-year-old woman was followed-up for 15 years clinically and paraclinically after a heavy PHT intoxication. Her immunoglobulins in serum were checked on PHT and after 15 years treatment with carbamazepine. RESULTS-A gross mass of hyperplasia tissue found primarily in the left side of her mouth had disappeared and serum IgA which was subnormal at the first visit had normalized. CONCLUSION-It is possible to prevent GH from PHT treatment by intensive dental care, correct mouth hygiene and by change of treatment of carbamazepine.