Multiple endocrine neoplasm type 1 (MEN1) is associated with parathyroid, pancreatic, and pituitary tumors. Although most patients present with hyperparathyroidism, the diagnosis can be difficult, because a significant proportion present with other endocrinopathies or may lack a family history, and other MEN1 manifestations may be mild. Recently, multiple cutaneous lesions (angiofibromas and collagenomas) were reported to be frequent in MEN1 patients, and it was proposed that their discovery suggested the diagnosis of MEN1. The purpose of this study was to prospectively assess the frequency and sensitivity/specificity of various cutaneous criteria for MEN1 in 110 consecutive patients with gastrinomas with or without MEN1. All patients had hormonal and functional studies to determine MEN1 status (48 with MEN1, 62 without MEN1), dermatological evaluation, and tumor imaging studies. Angiofibromas and collagenomas were more frequent in MEN1 patients (64% vs. 8% and 62% vs. 5%; P < 0.00001) and were multiple in 77-81% of the MEN1 patients. Lipomas occurred in 17%. The presence of these skin lesions did not correlate with age, disease duration, or other MEN1 features. Angiofibromas or collagenomas (single or multiple) had 50-65% sensitivity for MEN1 and 92-100% specificity. The combination criterion of multiple angiofibromas (more than three) and any collagenomas had the highest sensitivity (75%) and specificity (95%). This criterion has greater sensitivity than pituitary or adrenal disease and is comparable to hyperparathyroidism in some studies of patients with MEN1 with gastrinoma. This criterion should have sufficient sensitivity/specificity to be clinically useful.