After transnasal operations in Cushing's syndrome persisting hypercortisolism either due to negative pituitary exploration or due to subtotal tumor removal, and recurrence of the disease after successful surgery still are challenging. We report on the therapeutic failures among 310 consecutive patients who underwent primary transsphenoidal microsurgery for Cushing's disease. In 287 patients an ACTH-producing pituitary adenoma could be detected (finding rate: 92.6%). In 264 cases remission of hypercortisolism could be attained (remission rate with adenoma 92.0%, for the whole series of primary operations 85.2%). In 23 patients no adenoma could be found despite extensive pituitary exploration (7.4%). Here, we will focus on the management of the 23/287 patients with persistent hypercortisolism after transnasal tumor operation (8.0%) and those 29 cases of the 264 patients with a remission who developed a recurrence of hypercortisolism (11.0%). In recurrent hypercortisolism we recommend transsphenoidal reoperation even when no tumor is visible in MRI. Seventeen of 24 reoperations in recurrent Cushing's disease were successful (70.8%). In persistent hypercortisolism we perform a reoperation during the same hospital stay. Nine of 16 early reoperations led to remission of hypercortisolism (56.3%). If transsphenoidal reoperation fails we indicate radiation therapy of different modalities depending on the extension and location of the tumor remnants. Bilateral adrenalectomy is proposed by us only if all other therapeutic measures failed.