Phenytoin (diphenylhydantoin or Dilantin) is a highly effective and widely prescribed anticonvulsant agent used in the treatment of grand mal and psychomotor epilepsy. In dermatology, phenytoin has been used to treat ulcers, epidermolysis bullosa, and inflammatory conditions. Its mechanism appears to involve its ability to inhibit collagenase. Its topical use for the promotion of wound healing seems promising but requires further trials. The side effects of phenytoin continue to create significant morbidity. Common side effects include gingival hyperplasia, coarsening of the facies, and hirsutism. Rarer cutaneous side effects include drug-induced lupus, purple-hand syndrome, pigmentary alterations, and IgA bullous dermatosis. It can cause generalized cutaneous eruptions that include a maculopapular exanthem, Stevens-Johnson syndrome, generalized exfoliative dermatitis, toxic epidermal necrolysis, vasculitis, and fixed-drug eruptions. Phenytoin is linked to a hypersensitivity syndrome manifested by fever, rash, and lymphadenopathy. Patients receiving phenytoin may develop pseudolymphoma or, rarely, malignant lymphoma and mycosis-fungoides-like lesions. Phenytoin can effect clotting function. Phenytoin can alter vitamin and mineral levels. Prenatal exposure to phenytoin may result in a spectrum of structural, developmental, and behavioral changes known as the fetal hydantoin syndrome. After 60 years of use, phenytoin uses and mechanisms of action have yet to be fully defined; the drug remains a useful tool and an important subject for additional research.