The syndrome of multiple endocrine neoplasia type 1 is an autosomal dominantly inherited disease affecting several endocrine organs. The affected organs include the pituitary, the parathyroids and endocrine pancreas, where different types of lesions can be found, such as hyperplasia or frank carcinomas. The most life threatening lesions are the endocrine pancreatic tumors, which cause about 80% of all deaths among the MEN-1 members. In our own series of 108 members from 16 families with multiple endocrine neoplasia, 55 members had the MEN-1 trait. Among these members, pituitary lesions were found in 42%, parathyroid involvement in 89% and endocrine pancreatic tumors in 58%. Hyperparathyroidism was the presenting lesion of the MEN-1 trait. By using a specific meal stimulation test we have been able to unveil pancreatic lesions up to a median of five years previous to radiological detection. Very recently we have been able to detect a specific genetic lesion in MEN-1 members by studying DNA rearrangements with recombinant DNA technique, using the method of polymorphic restriction enzyme recognition in three large kindreds. The MEN-1 locus maps to chromosome 11q and the MEN-1 predisposition would be a constitutional mutation in heterozygous form, inherited as an autosomal dominant trait. Tumor development involves a second mutational event which involves the chromosome 11, carrying the remaining 'wild' type allele at the MEN-1 locus by means of chromosome loss event. Survival analysis demonstrates that patients with the MEN-1 syndrome had a significantly better survival from diagnosis than patients with sporadic endocrine pancreatic tumors (median 15.1 years and 5.8 years respectively, p = 0.0068). Earlier diagnosis and start of treatment might account for a longer survival in the MEN-1 group, but a possibility of differences in tumor biology between familial and sporadic endocrine pancreatic tumors cannot be ruled out. The surgical treatment of patients with MEN-1 include resection of the parathyroids with transplantation of a piece of the gland to the forearm, resection of endocrine pancreatic tumors in the tail and local enucleation of tumors in the pancreatic head and body. Total pancreatectomy should be avoided in most instances. The causative medical treatment of patients with malignant endocrine pancreatic tumors and the MEN-1 trait include chemotherapy (streptozotocin plus 5-fluorouracil), interferons and the somatostatin analogue SMS 201-995.