<prompt> The most common organ involved in MEN I is -ParathyroidThyroidAdrenalTestis  <response>: 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 30-70Pituitary adenoma 15-50Adrenal coical tumor 20-70, Pheochromocytoma1, Bronchopulmonary NET2, Thymic NET2, Gastric NET10, Lipomas33, Angiofibromas85, Collagenomas70, Meningiomas8 Reference : page 2336 Harrisons Principles of Internal Medicine 19th edition 