RAD51 - a DNA double-strand breaks repair gene plays an important role in homologous recombination, a process frequently involved in cancer transformation. The aim of this study was to compare the distribution of the genotype of the RAD51 G135C polymorphism between colorectal cancer (CRC) patients and controls. We also tested the association between the G135C polymorphism of the RAD51 gene and the risk of CRC, and various clinicopathological parameters. Polymorphism was evaluated by restriction fragment length polymorphism PCR in 100 CRC patients and 120 age-matched and sex-matched controls. There was a significant association between RAD51 genotypes and CRC cases (P<0.05). Also, the GC genotype was associated with an increased risk of CRC (odds ratio >3.84). Our results suggest that the G135C polymorphism of the RAD51 gene is associated with an increased risk of CRC in our population.