Seven hundred forty-four eyes with very severe proliferative diabetic retinopathy (PDR) were followed with conventional management over a two-year period. Decreases in visual acuity were more frequent during the first year of follow-up than during the second, and were related to baseline visual acuity level and retinopathy severity. After two years, visual acuity was less than 5/200 in 45% of eyes with more than four disc areas of new vessels and visual acuity of 10/30 to 10/50 at baseline, but in only 14% of eyes with traction retinal detachment not involving the center of the macula and without active new vessels or fresh vitreous hemorrhage at baseline. Vitrectomy, which was undertaken only if retinal detachment involving the center of the macula occurred or if severe vitreous hemorrhage failed to clear after a one-year waiting period, had been carried out in 25% of eyes after two years of follow-up.