Multiple endocrine neoplasia syndrome type 1 (MEN-1) is an inherited disorder characterised by the predisposition of the cells from parathyroid glands, endocrine pancreas and adenohypophysis to develop neoplasms. We report the genetic study of an extended family with at least 8 affected patients and 10 putative carriers of a mutation in MEN-1 gene. One intragenic (Asp418 GAC-->GAT), and five flanking markers were characterised in the family by PCR amplification and polyachrylamide gel electrophoresis. Association of the disease to MEN-1 gene was confirmed for this family: all the affected members show a haplotype in common. Three patients at risk were diagnosed as non-carriers, since they have not inherited that haplotype. The remaining seven members, presymptomatic carriers, are included in a follow-up protocol. The genetic study of families segregating MEN-1 syndrome are useful in avoiding indiscriminate follow-up determinations to those members who have not received the genetic predisposition to develop any of the manifestations of the syndrome. Segregation analysis with linked markers is useful, under certain circumstances, to perform such type of studies.