1. Renal artery disease is a potentially dangerous condition with 5 year mortality rate around 30% whether treated medically or surgically, and reduction of blood pressure to normal levels does not offer complete protection from cardiovascular death. 2. The mortality rate is relatively low in the first four decades, but rises rapidly after this. Length of history is not closely related to the prognosis. 3. No single diagnostic criterion is of over-riding importance in assessing operability and prognosis, but evidence of secondary hypertensive damage to the contra-lateral kidney indicates a bad result. 4. Fibroplasia stenosis offers a much better prognosis than atheroma. 5. Operative treatment is suggested as the method of choice for patients in the first four decades with anatomical and functional evidence of stenosis provided there is no evidence of secondary hypertensive renal damage. In other patients medical treatment is suggested primarily although surgery may salvage a small proportion of patients in whom this treatment is unsuccessful.