AIM: To analyze the genotype of the allele distribution of a polymorphic G-954C within the 5' upstream promoter region of the nitric oxide synthetase 2A gene (NOS2A ) in samples of diabetic retinopathy in patients with cystoid macular edema in the mainland of China. · METHODS: Eighty-nine patients with diabetic retinopathy and cystoid macular edema and 90 healthy controls were enrolled in this study. Nest polymerase chain reaction (PCR) was performed, and restriction endonuclease digestion and gene fragments sequence were examined to detect the genotype of NOS2A G-954C. · RESULTS: The genotypes of the sample population of 89 cases and 90 healthy controls were all detected as GG. · CONCLUSION: The distribution of G-954C of NOS2A polymorphism are at a lower frequency in China, with little relevancy to the frequency of diabetic retinopathy combined with cystoid macular edema.