Additional follow-up confirms previous reports from the Diabetic Retinopathy Study (DRS) that photocoagulation, as used in the study, reduces the risk of severe visual loss by 50% or more. Decreases of visual acuity of one or more lines and constriction of peripheral visual field due to treatment were also observed in some eyes. These harmful effects were more frequent and more severe following the DRS xenon technique. The two-year risk of severe visual loss without treatment outweighs the risk of harmful treatment effects for two groups of eyes: (1) eyes with new vessels and preretinal or vitreous hemorrhage; and (2) eyes with new vessels on or within one disc diameter of the optic disc (NVD) equaling or exceeding 1/4 to 1/3 disc area in extent, (Fig 1), even in the absence of preretinal or vitreous hemorrhage. For eyes with these characteristics, prompt treatment is usually advisable. For eyes with less severe retinopathy, DRS findings do not provide a clear choice between prompt treatment or deferral unless progression to these more severe stages occurs.