The prevalence of focal and panretinal photocoagulation and its relationship to demographic and other characteristics were examined in a population-based study in southern Wisconsin. For participants whose age at diagnosis was less than 30 years and who were taking insulin (996 persons) the prevalence rate of panretinal photocoagulation (13.9%) was higher than that of focal photocoagulation (3.6%). For those whose age at diagnosis was 30 years or older (1370 persons), the prevalence rate for panretinal photocoagulation (3.6%) was slightly higher than that of focal photocoagulation (3.0%). Seventy-two percent of eyes of younger onset and 45% of eyes of older onset persons that had received panretinal photocoagulation treatment were found to have incomplete regression of retinal new vessels, and in approximately half of these eyes severe proliferative retinopathy (Diabetic Retinopathy Study High Risk Characteristics [DRS-HRC]) was present. Among eyes with DRS-HRC, 55% were found to be untreated.