Background:The endothelial nitric oxide synthase (eNOS) gene encodes the eNOS enzyme in humans; it synthesizes nitric oxide (NO), which prevents or promotes colorectal cancer (CRC) progression. Polymorphisms of eNOS are correlated with the probability of cancer, but the findings are not consistent. Objectives: The present study aimed at investigating the correlation of eNOS rs1799983 polymorphism with CRC compared to the control group. Methods: The eNOS rs1799983 polymorphism (G894T) was assessed in 100 healthy control subjects and 100 patients with CRC. Polymerase chain reaction (PCR) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) were utilized to analyze the eNOS polymorphism. Results: The risk of CRC in genotypes TT and GT of eNOS G894T polymorphism was significantly greater than genotype GG. The frequencies of genotypes TT and GT were 6% and 37% in the controls and 28% and 44% in the patients, respectively. The frequency of TT and GT genotypes showed a significant difference between patients with CRC (adjusted odds ratio (OR = 3.1, 95% confidence interval (95% CI) = 1.6 -3.2; P = 0.001) and controls (adjusted OR = 1.8, 95% CI = 0.6 -2.5; P = 0.005). Conclusions: According to the results of the present study, allele T of eNOS G894T had a significant correlation with CRC even after adjusting for traditional risk factors.