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Background: Abnormalities of the pupil of the eye are well known in long-term diabetes. Anyone who has been engaged in fundoscopic exarninations of diabetics is familiar with the occasional difficulty caused by insufficient dilation of the pupil in these patients with parasympathicolytic agents. In the present study, the pupil size in darkness is measured in a large group of diabetics to further investigating the occurrence of diminished pupil size in diabetes and to define the relationship of this abnormality to the duration and degree of metabolic aberration and to other chronic complications. Methods : The pupil size was measured in darkness by portable electronic pupillometer in 214 diabetics, aged 28-76 years, diabetes duration 0-25 years. Pupillometry was performed in the left eye with an infrared computerized pupillometer(Pupilscan). All study participants were assessed using five standard cardiovascular tests (maximum-minimum heart rate during deep breathing, heart rate change during a Valsalva maneuver, lying-to-standing heart rate change, lying-to-standing BP change, and BP change after handgrip exercise). We used Autocaft software for the tests. As a measure of peripheral somatic nervous function the peroneal nerve conduction velocities were estimated by means of a Quantum model 'Q84'. Glycated hemoglobin was measured with a colorimetric method. Retinopathy was assessed with stereofundal photography and elassified as background retinopathy and proliferative retinopathy. Nephropathy was classified as normoalbuminuria. microalbuminuria and macroalbuminuria groups. Results : Pupil diameters were significantly smaller with longer duration of diabetes(r=-0.20, p<0.001), and higher levels of glycated hemoglobin(r=-0.l5, p<0.004). There was an inverse correlation between pupil diameter and autonomic test score(r=-0.44, p<0,001). Pupil diameters become smaller with decreasing peroneal nerve conduction velocity(r = 0.21, p < 0.001). The results revealed significant relationship between the pupil diameter and severity of abnormalities in retinopathy(p<0.001), and nephropathy(p<0,001). Conclusion : The results revealed pupil diameters were significantly smaller with longer duration of diabetes, higher glycated hemoglobin values, and higher grades of chronic complications.