Fifty eyes with three or four diabetic retinopathy risk factors received argon laser panretinal photocoagulation (PRP) with treatment randomly assigned to either central or peripheral distribution. Six months after treatment, two or more acuity lines had been lost by 24% of the central PRP, and by only 8% of the peripheral PRP eyes. Mean visual field constriction with the I-4e isopter was 39% for the central and 29% for the peripheral PRP eyes; for the IV-4e isopter, it was 12 and 7%. Pretreatment macular thickening increased in 19% of the central PRP eyes, but decreased in 19% of the peripheral PRP eyes (P less than 0.05). There was complete disc neovascular regression in 38% of the central and 47% of the peripheral PRP eyes. Partial regression was obtained in 31% centrally and 33% peripherally treated eyes.