We have experienced 3 cases in 2 families of multiple endocrine neoplasia (MEN) type IIa. Case 1: 61 year-old female underwent her first operation of right hemithy roidectomy for thyroid cancer followed by her second of right adrenalectomy later added thereto for pheochromocytoma as diagnosed. In the meantime, her cousin was found to have undergone an operation at another hospital for the same disease. She was further diagnosed as medullary carcinoma of thyroid gland (MCT) in her left thyroid gland and a total thyroidectomy was performed. Case 2: 33 year-old female had a chief complaint of palpitation and was introduced to our 2nd Department of Surgery for suspection of pheochromocytoma. It was found to be of MEN type IIa after various tests. Bilateral adrenal glands of pheochromocytoma were removed followed by a total thyroidectomy performed 47 days later. In the family study of case 2, MCT was detected in her eldest brother and identified as familial type. This case 3, 49 year-old male had no parathyroid disease or pheochromocytoma and total thyroidectomy was performed for MCT.