PURPOSE Diabetic retinopathy and nephropathy are microvascular complications in patients with diabetes that are considered to be related. Pigment epithelium-derived factor (PEDF), a strong inhibitor of angiogenesis, is significantly elevated in the blood of diabetic patients, especially those with proliferative diabetic retinopathy (PDR). The level of PEDF in the blood, on the other hand, is reported to be low in a diabetic nephropathy. The aim of this study was to determine the relationship between PEDF and renal function in patients with diabetic retinopathy. METHODS A total of 243 type 2 diabetic patients were studied. The relationship between the diabetic retinopathy and levels of PEDF, HbA1c, blood urea nitrogen (BUN), and creatinine were evaluated. RESULTS The mean plasma PEDF level in patients with PDR (7.69+/-6.14 microg/ml; mean+/-standard error) was significantly higher than that of mild-to-moderate nonproliferative diabetic retinopathy (5.07+/-4.37 microg/ml, p=0.02). The level of BUN and creatinine increased significantly as the stage of diabetic retinopathy advanced. The plasma PEDF levels were significantly correlated with the levels of BUN and creatinine (r=0.54, p<0.0001; r=0.57, p<0.0001, respectively). CONCLUSIONS The levels of plasma PEDF increases with advances in both diabetic retinopathy and nephropathy. Thus, increased levels of PEDF in the blood may indicate microvascular damages in diabetic patients and may be predictor of the progression of retinopathy and nephropathy.