Objective To evaluate the relationship between metabolic syndrome (MetS) and the prevalence of diabetic retinopathy (DR). Research Design and Methods We conducted a case-controlled study, with data obtained from 2,551 Chinese participants between 18-79 years of age (representing a population of 1,660,500 in a district of Beijing). 74 cases of DR were found following data assessment by two 45 degrees digital retinal images. Subjects without DR (NDR group) selected from the remaining 2,477 subjects were matched 1:1 to the DR group by HbA1c. MetS was defined by incorporating diagnostic criteria of the American Heart Association/National Heart, Lung, and Blood Institute (AHA/NHLBI) and the International Diabetes Federation (IDF). Results There were no statistical differences between the DR group and NDR group in a number of biological or laboratory tests. However, the percentage of patients with DR increased vs. patients without DR with the number of MetS components from 1 to 5 (14.3% vs. 85.7%, 38.9% vs. 61.1%, 49.1% vs. 50.9%, 61.4% vs. 38.6% and 83.3% vs. 16.7%, respectively) (Pearson chi(2) = 9.938, P = 0.037). The trend to develop DR with MetS was significantly higher than that without MetS (NMetS) (chi(2) = 5.540, P = 0.019). MetS was an independent statistical indicator of the presence of DR after adjusting for age and sex [odds ratio (95% CI): 2.701 (1.248-5.849), P = 0.012], which is still the case with an additional adjustment for WC, SBP, TC, HbA1c and duration of diabetes [odds ratio (95% CI): 2.948(1.134-7.664), P = 0.027]. Conclusion DR is one of the diabetic microvascular complications. Apart from poor glycemic control, the concomitance of other metabolic factors can also influence DR. MetS, defined as a cluster of metabolic risk factors, is a strong and independent indicator of DR, even to the same extent as glycemic control.