Details of health, with particular reference to endocrinopathy, were acquired on all living and decreased members of a 4 generation family. Five members were found to be affected with MEA-I. Hyperparthyroidism was the most frequently diagnosed endocrinopathy, but pancreatic tumors were also found to be involved. No indications of the involvement of pituitary tumors were observed. A mediastinal tumor accompanied by a thymoma was also observed. None of the children under 18 years of age were affected. Genetic analysis confirmed the concept that the syndrome follows an autosomal dominant mode of inheritance with virtually complete penetrance but variable expressivity. A careful investigation at regular intervals of high risk members of an affected family is recommended for proper medical management of the condition.