Three patients with familial multiple endocrine neoplasia type 2 underwent total adrenalectomy and subsequently near-total or total thyroidectomy. The overt pheochromocytomas were present bilaterally in two patients and unilaterally in another patient. In addition, multiple nodules measuring a few mm in diameter were demonstrated in all adrenal medullas examined. All patients exhibited bilateral medullary thyroid carcinomas which varied in size from a few minute nodules accompanied by the microscopic C-cell hyperplasia to distinct large tumors. The thyroid C-cell hyperplasia appeared to be confined to the upper and middle thirds of the lateral lobe, and micronodules of the C-cell hyperplasia enlarged to coalesce, forming one large carcinoma mass. On the other hand, nodular hyperplasia of the chromaffin cells was distributed diffusely throughout the adrenal medulla and each nodule appeared to develop individually into a large pheochromocytoma. These findings suggested that, at least in the family members at a high risk for multiple endocrine neoplasia type 2, the development of both medullary thyroid carcinoma and pheochromocytoma was always preceded by a multicentric nodular hyperplasia. On the basis of the pathogenesis of these tumors, the most rational surgical approach was presented.