This study tests the hypothesis that subjects with proliferative diabetic retinopathy (PDR) have a detectable rise in levels of serum vascular endothelial growth factor (VEGF), which is an important regulator of angiogenesis. Our investigation aims to evaluate plasma VEGF changes after pan-retinal photocoagulation (PRP) in diabetic patients. Twenty-nine type two diabetic patients (17 male, 12 female: mean age 53.13±12.22 years) with PDR secondary to diabetes were studied. Blood samples were obtained before and at 2 months after the last PRP session. Serum VEGF levels were measured by ELISA. After PRP, the mean serum VEGF decreased, but this reduction was not remarkable (88.68±71.09 vs. 77.01±60.33 ng/ml) (P=0.18). There was a statistically significant difference in serum VEGF changes between patients who had regressed PDR with patients who had progressed PDR (-25.98±47.37 vs. 56.44±31.7 ng/ml) (P=0.003). Our results showed a significant reduction in levels of serum VEGF in the patients who had successful laser treatment. Our findings suggest that serum VEGF levels could be used for monitoring diabetic retinopathy outcome.