The pathogenetic process of diabetic retinopathy and the role of different systemic risk factors in IDDM and NIDDM is not completely understood. The aim of the present cross-sectional clinical study was (1) to compare the prevalence of systemic risk factors for diabetic retinopathy in IDDM and NIDDM patients, (2) to determine relations between these risk factors and the degree of retinopathy and (3) to evaluate the relationship between retinopathy and neuropathy. The study included 1,218 IDDM and 784 NIDDM patients attending our hospital during 1994. The mean diabetes duration was 15.4 and 13.2 years, respectively. IDDM patients with proliferative retinopathy were characterized by higher mean age of 46.4 +/- 1.08 vs. 21.8 +/- 0.42 years and longer diabetes duration of 30.0 +/- 0.79 vs. 7.7 +/- 0.26 years. Among the NIDDM patients, those ones with proliferative retinopathy had the lowest mean age of 40.5 +/- 1.42 vs. 49.7 +/- 0.61 years (p < 0.01) at diabetes manifestation. There was no statistical difference between mean HbA1c concentrations in relation to retinopathy stages. Albumin excretion was increased in both IDDM and NIDDM patients with proliferative retinopathy (p < 0.01) along with increased BMI of IDDM and increased insulin requirement of NIDDM patients (p < 0.01). Multiple regression analysis showed that proliferative retinopathy with the inclusion of non-proliferative retinopathy of IDDM and NIDDM patients was significantly correlated with diabetes duration, albumin excretion, somatic and autonomic neuropathy (p < 0.01). In NIDDM patients proliferative retinopathy with the inclusion of non-proliferative retinopathy was correlated with the age at diabetes manifestation and with cholesterol levels (p < 0.05). In IDDM and NIDDM patients proliferative retinopathy was found to be correlated with somatic and autonomic neuropathy, albumin excretion (p < 0.01) and hypertension (p < 0.05). The importance of the significant correlation of autonomic neuropathy both with background and proliferative retinopathy in IDDM and NIDDM patients needs to be prospectively investigated.