BACKGROUND The treatment of choice for Cushing's disease is pituitary surgery. Second-line treatments include repeat pituitary surgery, radiation therapy, medical therapy, and bilateral adrenalectomy. The most used modalities to irradiate patients with Cushing's disease include fractionated radiotherapy and single-dose Gamma Knife. We aim to review the efficacy and safety of radiotherapy in patients with persistent or recurring Cushing's disease. RESULTS Remission of Cushing's disease after radiotherapy ranges from 42 to 83%. There seems to be no clear difference according to the technique of radiation used. Most patients experience remission of disease within 3 years from treatment, with only few cases reaching normal cortisol secretion after a longer follow-up. Control of tumor growth varies from 93 to 100%. Severe side effects of radiotherapy, such as optic neuropathy and radionecrosis, are uncommon. New-onset hypopituitarism is the most frequent side effect of radiation, occurring in 30-50% of patients treated by fractionated radiotherapy while it has been reported in 11-22% of patients after Gamma Knife. CONCLUSIONS Radiotherapy is an effective second-line treatment in patients with Cushing's disease not cured by surgery. Consideration of the advantages and disadvantages of radiotherapy in comparison with other therapeutic options should always be carried out in the single patient before deciding the second-line therapeutic strategy for persisting or recurring Cushing's disease.