PURPOSE To determine the relationship between the severity of diabetic retinopathy and the levels of interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF) in aqueous humor and plasma. METHODS Forty-four eyes of 34 diabetic patients were studied. The concentrations of VEGF and IL-6 in plasma samples and in aqueous specimens obtained from the eyes during cataract surgery were measured by enzyme-linked immunosorbent assay. RESULTS Aqueous levels of VEGF and IL-6 were significantly correlated with the severity of diabetic retinopathy (p = 0.793 and p = 0.744, respectively). Vascular endothelial growth factor and IL-6 levels in aqueous humor were significantly correlated with the aqueous protein concentration (p = 0.641 and p = 0.646, respectively). The aqueous level of VEGF was significantly correlated with that of IL-6 (p = 0.627). Aqueous levels of VEGF and IL-6 were also significantly correlated with the grade of fundus findings. Vascular endothelial growth factor and IL-6 concentrations were higher in the aqueous than in the plasma. CONCLUSION The results of the current study suggest that there is a relationship between VEGF and IL-6 but the role of IL-6 in diabetic retinopathy is unclear and may warrant further investigation.