The lethality of the endocrine tumors associated with multiple endocrine neoplasia type I (MEN-I), particularly the pancreatic islet cell tumors, has been controversial. We evaluated the cause and age of death in MEN-I kindreds. Our database contains 34 distinct kindreds with 1838 members. Reliable death data are available for 103 people (excluding accidents and age < 18 years). We compared survival curves of MEN-I patients who died from causes related to MEN-I with those from MEN-I carriers who died from a nonendocrine cause and unaffected kindred members. We also compared ages of death between affected and unaffected members of MEN-I kindreds. Of 59 MEN-I-affected patients, 27 died directly of MEN-I-specific illness and 32 of non-MEN-I causes. The MEN-I-specific deaths occurred at a younger age (median 47 years) than either MEN-I patients whose death was from some nonendocrine cause (median 60 years, p < 0.02) or than all kindred members who did not die of MEN-I disease (median 55 years, p < 0.05). The causes of death of the MEN-I patients included islet cell tumor (n = 12), ulcer disease (n = 6), hypercalcemia/uremia (n = 3), carcinoid tumor (n = 6), and nonendocrine malignancies (n = 9). There was no difference in survival between MEN-I carriers and unaffected kindred members. Of our MEN-I patients, 46% died from causes related to their endocrine tumors after a median age of 47 years, which was younger than family members who did not die from these tumors. Pancreatic islet cell tumors were the most common cause of death of MEN-I patients. Management of kindreds with MEN-I should include an aggressive screening program with early therapeutic intervention when a tumor is identified.