The occurrence of retinopathy and its relationship to diabetes in 1,640 Pima Indians age 15 and over has been determined. Eighteen per cent of those with two-hour postload plasma glucose levels of equal to or greater than 200 mg./dl. had some evidence of retinopathy. Of those with retinopathy and diabetes, 7 per cent were found to have proliferative or neovascular changes, the remainder having microaneurysms and/or exudates. The frequency of retinopathy increased from 3 per cent among newly diagnosed diabetics to 47 per cent among those with diabetes of 10 or more years duration. No relationship was found with sex, age at diagnosis of diabetes, or age at time of examination when duration of diabetes was taken into account. The occurrence of retinopathy was confined largely to those who fell into the second or hyperglycemic component of the frequency distribution of plasma glucose levels in the population, indicating the significance of the bimodal glucose tolerance frequency distribution.