The results of Farnsworth-Munsell 100-hue, visual acuity, and visual field testing were compared with the severity of retinopathy in a group of 90 diabetic patients. The patients showed significantly higher than expected Farnsworth-Munsell 100-hue scores, with a tritanlike axis, compared with published age norms for nondiabetic individuals. The magnitude of the acquired blue-yellow hue discrimination defect correlated significantly and to a similar extent with both the severity of overall diabetic retinopathy and the severity of macular edema and hard exudate formation. Visual acuity loss correlated somewhat more significantly with macular edema than with overall retinopathy, whereas the converse was true for visual fields. For all visual function tests, the correlations were more significant for fluorescein leakage in the macula than for capillary nonperfusion in the macula. Abnormal hue discrimination was found in 65% (32/49) of eyes with proliferative diabetic retinopathy, suggesting a potential role for this test in screening for proliferative diabetic retinopathy in primary care facilities. Also, because the ability of diabetic patients with color vision deficiency to perform color-dependent tests for urinary and blood glucose may be impaired, such patients should be made aware of this potential problem.