The incidence of moderate visual impairment and blindness due to diabetic retinopathy was studied 5 years after introducing a screening system for early detection of treatable retinopathy. Photocoagulation was performed in patients with clinically significant macular oedema, severe preproliferative, and proliferative retinopathy. Eighty-eight percent of 470 Type 1 and 88% of 388 Type 2 diabetic patients were still available for follow-up. In the Type 1 group, the five-year incidence of blindness and moderate visual impairment were 0.5% and 1.2%, respectively. Corresponding figures for the Type 2 diabetic patients were 0.6% and 1.7%, respectively. The majority of patients with loss of vision had severe retinopathy at baseline. Among those who entered the screening programme with no or mild retinopathy, loss of vision occurred in only one of the Type 1 and four of the Type 2 diabetic patients. It is concluded that the risk for visual impairment and blindness due to diabetes can be substantially reduced by using programmes for early detection of and effective treatment of diabetic retinopathy.