Contrast sensitivity has been assessed in 24 diabetic patients in order to test the hypothesis that contrast sensitivity is impaired in the early stages of diabetes mellitus. All patients had 20/20 vision. Some evidence of visual dysfunction was observed in 33% of the diabetics with no retinopathy and 83% of the 6 patients with retinopathy when compared to 48 age-matched controls. Contrast sensitivity was mainly reduced in the mid-range spatial frequencies and correlated with the degree of retinopathy. The accurate assessment of visual dysfunction in diabetes is very important, as new drugs (i.e. aldose reductase inhibitors) are currently under evaluation.