The most common organ involved in MEN I is -

Primary hyperparathyroidism (parathyroid gland) occurs in approximately 90% of patients and is the most common feature of MEN 1. Other organs involved are- * Enteropancreatic tumor (30-70%)*Pituitary adenoma (15-50%)*Adrenal coical tumor (20-70%), Pheochromocytoma(<1%), Bronchopulmonary NET(2%), Thymic NET(2%), Gastric NET(10%), Lipomas(>33%), Angiofibromas(85%), Collagenomas(70%), Meningiomas(8%) Reference : page 2336 Harrison's Principles of Internal Medicine 19th edition