We measured the corneal autofluorescence in groups with different levels of diabetic retinopathy severity (72 eyes of 46 patients) and in age-matched non-diabetic controls (34 eyes of 24 controls). We also estimated the corneal endothelium cell count and pachymetry with a contact specular microscope. For the controls, mean corneal autofluorescence was 8.8 ng equivalents fluorescein/ml (SD 0.3). Results showed increased autofluorescence of the cornea in diabetic patients (mean 17.9 ng equivalents fluorescein/ml, SD 4.2), related to the duration of diabetes (P < 0.05) and to the severity of diabetic retinopathy (P < 0.0001). Corneal endothelial cell count results showed no statistically significant relation to corneal autofluorescence (P < 0.6), indicating that the increased autofluorescence cannot be attributed to a change in corneal cell density.