External radiotherapy (ideally 3-field radiotherapy with a daily fractional dose no higher than 1.8 Gy or conformal irradiation) has been used extensively in the treatment of acromegaly, and virtually all studies have documented a predictable but slow reduction in growth hormone (GH) excess, which is at its maximum in the first year after treatment (30-50%) and continues at an average rate of 10-15% thereafter in the long term. Therefore, achievement of 'safe' GH concentrations in an acceptable time interval after radiotherapy will be realized only in those patients who have lower GH concentrations prior to irradiation either as a result of mild disease or previous surgery. Recent studies have demonstrated the value of stereotactic radiotherapy (either as multiple arc X-irradiation or as 'gamma knife' therapy) in the post-surgical treatment of acromegaly or as salvage therapy for disease persisting after conventional external irradiation. The development of potent medical therapies for acromegaly (somatostatin analogues and the GH receptor antagonist) has called into question the role of radiotherapy in the treatment of this disease. However, even if the concept of primary, open-ended medical therapy for selected patients is accepted, reference to the success rates of surgery and response rates to somatostatin analogues indicates that approximately 10-20% of all patients with acromegaly will require consideration of radiotherapy for hormonal or tumour mass control. For these reasons, radiotherapy (both conventional external and stereotactic irradiation) continues to have a major role in controlling acromegaly in selected patients.