Our findings from a well-characterized cohort of 162 index patients with genotype-positive MEN1 and 47 patients with genotype-negative disease verify that patients with genotype-positive disease have a distinct clinical course with multigland or recurrent parathyroid tumors, higher frequency of dpNETs, younger age at initial presentation with MEN1-related manifestation, and the presence of angiofibromas or collagenomas. This evidence concerns the gene MEN1 and tumor of parathyroid gland.