The change of aminoacid Arginine (CGG) to Glutamine (CAG) at position 171 (R171Q) in the MEN1 gene has been occasionally reported in MEN1 carriers, but also in 1.4 to 5% subjects among the general population, therefore it is still unclear whether it might represent a polymorphism and/or it has a role in tumourigenesis. The aim of our study was to evaluate the presence of the R171Q polymorphism in patients with MEN1-related states presenting for MEN1 genetic screening. Fifty-seven patients (16 men, 41 women, mean age 55.1±2.3) were evaluated for the R171Q polymorphism, that was detected in 1 patient presenting with a parathyroid adenoma and an ACTH-secreting pituitary adenoma, in her two sons, and in her father. The R171Q polymorphism was found in an unrelated patient with parathyroid adenoma and mild hyperprolactinemia, in her unaffected father, and in a third patient with parathyroid adenoma and paraganglioma. Moreover, the same polymorphism was found in an unrelated family, with primary hyperparathyroidism, non-functioning pancreatic neuroendocrine tumour and a non-functioning adrenocortical adenoma. As controls, a panel of 50 healthy subjects from the same geographical area was screened, and the R171Q aminoacid change was not detected. The R171Q was present in 8 out of 57 (14%) patients undergoing MEN1 genetic screening, in 34.8% of the cases presenting with hyperparathyroidism. Our results indicate that MEN1 patients carrying this genetic alteration, as well as clinically unaffected carriers, should undergo a careful endocrine investigation and a close clinical and biochemical follow-up.