This report describes clinical, biochemical and molecular findings regarding two Italian monozygotic twins carrying a novel multiple endocrine neoplasia type 1 (MEN1) mutation inherited from their mother.Clinical, biochemical and genetic evaluations of the above-mentioned family members were performed.All three members were heterozygous for a deletion involving the first nucleotide at codon 98 in exon 2 of the MEN1 gene, which results in early termination of the protein. The clinical phenotypes were as follows: one out of the two twins suffered from insulinoma and hyperparathyroidism, while the second one was asymptomatic. Furthermore, the mother suffered from hyperparathyroidism, as well as from hypergastrinemia for several years before the daughter was diagnosed of MEN-1.We describe a family with a new heterozygous mutation (g.292delC) in the MEN1 gene not described previously. The mutation leads to a truncated protein without activity, explaining the clinical picture of this family.