We describe a large multigenerational multiple endocrine neoplasia Type 1 (MEN1) family with clinical expression suggestive of anticipation. In the second and third generations, two deceased obligate gene carriers died at the ages of 85 and 76 without the history of MEN1, whereas two other living gene carriers above the age of 65 have had no clinical evidence of MEN1 to date. In the fourth generation, eight members were affected, with four having severe MEN1-related and atypical malignancies: a case of metastatic endocrine pancreatic tumor, two cases of metastatic thymic carcinoids, and a case of spinal ependymoma. In the fifth generation, all five patients were below the age of 22 when the disease was detected. MEN1 was confirmed in the family by linkage analysis using MEN1-linked microsatellite markers and by identification of a nonsense mutation in the MEN1/menin gene. Alleotyping showed loss of heterozygosity (LOH) involving the wild-type alleles in seven tumors in the family including the ependymoma, which is the first MEN1-related case that shows genetic abnormality in chromosome 11q13, suggesting that MEN1 gene might be involved in the tumorigenesis of a subset of ependymomas. In relation to clinical anticipation, repeated expansion studies were carried out but failed to detect any expansion. We conclude that this is a unique MEN1 family and that an unknown genetic mechanism might be contributing to the anticipation phenomenon. We demonstrate in this family that all gene carriers, including the very young members, will need close and careful follow-up.