Over 1500 MEN1 mutations have been reported, and 97% of these are associated with the simultaneous occurrence of the many tumours of the MEN1 syndrome, while the remaining 3% of mutations are associated with familial isolated hyperparathyroidism (FIHP), a disorder characterised by the sole occurrence of parathyroid tumours (5). Here, MEN1 is linked to familial isolated hyperparathyroidism.