The final results of a randomized controlled clinical trial of photocoagulation for diabetic maculopathy are reported, when all patients have been followed for at least 5 yr and some for as long as 7 yr. Ninety-nine patients with two similarly affected eyes had one eye chosen by a random procedure, treated with the xenon-arc photocoagulator; the untreated eyes remained as control. The mean visual acuity deteriorated by less than one line in treated eyes but by more than 2 lines in the controls (P less than 0.01). The difference in deterioration was greatest in patients whose initial vision was 6/6-6/9, and was not significant in those whose visual acuity was 6/36 or worse. Thirteen patients became blind in both eyes (visual acuity of 6/60 or less for 2 consecutive yearly assessments), 6 in the treated eye only, and 26 in the control eye only (P less than 0.01). Again the divergence between treated and control eyes was most marked in those whose initial vision was 6/6-6/9, (only one treated but 10 control eyes became blind). Hard exudates, microaneurysms, and hemorrhages improved more in the treated eyes (0.05 less than P less than 0.001) and more control eyes developed new vessels during the follow-up period. Twenty-three patients died during follow-up and another 16 failed to complete the study. Though the blood pressure of those who died was higher than those who survived (P less than 0.05 for both systolic and diastolic) no other medical abnormalities at entry had any clear effect on visual outcome or 5-yr survival. It is concluded that photocoagulation is of benefit in maintaining vision in diabetic maculopathy if the disease is not too far advanced.