One-hundred and forty patients with 182 treated eyes were followed for up to 10 years after photocoagulation for proliferative diabetic retinopathy. Sixty-eight patients were still alive and under review after 10 years. Mortality was 33% at 10 years and the survivors were younger when treated and had lower systolic and diastolic blood pressures, a lower urea and creatinine and a lower prevalence of proteinuria and ECG evidence of ischaemia at baseline. Sixty-nine percent of all patients and 82% of those followed up for 10 years maintained good vision (6/12 or better) in their better eye at the last follow-up. Visual deterioration occurred mostly in the first 2 years after treatment and risk factors for poor final vision were poor vision at baseline, severity of disc new vessels, and age at presentation. It is concluded that the short-term beneficial effect of photocoagulation is maintained over long periods of follow-up.