Ten patients with Nelson's syndrome, nine women and one man, aged 22 to 61 years, were treated neurosurgically by a transsphenoidal approach. In four patients, microadenomas were found, ranging in diameter from 4 to 10 mm. Microscopically, mixed adenoma was diagnosed in six cases, basophilic adenoma in three patients, and chromophobe adenoma in one patient. The presence of argyrophilic nerve fibers in the adenoma tissue was noted in one case. The time of observation after transsphenoidal surgery ranged from 6 months to 10 years. Clinical remission was achieved in eight patients; in two of them, radiation therapy was used to complement surgical treatment. In two patients, recurrence of the pituitary neoplasm was observed; anaplasia was revealed at the second operation in one of them. Radiation therapy might be a useful adjunct to neurosurgery in Nelson's syndrome, especially in patients with anaplastic adenoma.