Multiple endocrine neoplasia type I (MEN-I) is an autosomal dominant disorder characterized by endocrinopathies involving the anterior pituitary gland, parathyroid glands, and pancreas. The long-term prognosis for patients affected with this disorder is uncertain. To better characterize this prognosis, we performed a retrospective review of all patients with MEN-I treated at a single institution during the period 1951-1997. A group of 233 patients served as the study population. Their records were analyzed for confirmation of diagnosis, treatments received, long-term survival, and cause of death. Altogether, 108 eight male patients (46%) and 125 female patients (54%) were identified. At the conclusion of the study, 164 (70%) were alive and 69 (30%) were deceased, with a median follow-up for patients alive at last contact of 13.4 years (range < 1 month to 54.3 years). The cause of death was reliably obtained in 60 patients. Of these patients, 17 (28%) died of causes related to MEN-I, most commonly metastatic islet cell tumors (10 patients). The remaining patients died of causes unrelated to MEN-I, most commonly coronary artery disease and nonendocrine malignancies (14% each). The overall 20-year survival of MEN-I patients was 64% (95% CI was 56-72%), and that of an age- and gender-matched upper Midwest population was 81% (p < 0.001). Patients with MEN-I appear to be at increased risk of premature death. Earlier diagnosis and treatment of potentially malignant pancreatic islet cell neoplasms may result in a decrease of this premature mortality.