29 out of 39 patients bilaterally adrenalectomized for pituitary-dependent Cushing's syndrome between 1958 and 1979 have been followed up at regular intervals. ACTH-producing pituitary adenomas were detected and removed in 9 of them up to 1981. In 4 additional patients an enlarged sella turcica was already found at the time they had Cushing's syndrome, and therefore they were first treated by pituitary surgery or radiotherapy. In the adrenalectomized patients hyperpigmentation was the major clinical symptoms of the adenoma. Only in three instances did extrasellar growth of the adenoma cause ophthalmoplegia or narrowing of the visual fields. The existence of intrasellar ACTH-producing microadenomas in 5 additional patients seems highly probable in view of hyperpigmentation, excessively elevated plasma ACTH concentrations and radiological evidence of sella deformations. These observations indicate that in patients adrenalectomized for pituitary-dependent Cushing's syndrome ACTH-producing adenomas are more common than previously assumed. Moreover, according to recent reports, ACTH-producing microadenomas are frequently found in pituitary-dependent Cushing's syndrome and are assumed by many clinical endocrinologists to be the primary cause of this disease. Therefore, bilateral adrenalectomy is no longer the undisputed therapy of first choice and it is necessary in each individual case to consider carefully whether an attempt to remove selectively an ACTH-producing pituitary adenoma by microsurgery might not be preferable.