Background: Previous studies have observed an association between ABO blood group and risk for certaingastrointestinal malignancies, including pancreatic and gastric cancer. However, it is unclear whether thereis such an association with colorectal cancer (CRC). In this study, possible relationships between ABO bloodgroups and Rh factor and KRAS status in patients with CRC were investigated. Materials and Methods: In 1,620patients with CRC, blood group and Rh factor were examined and compared with the control group of 3,022,883healthy volunteer blood donors of the Turkish Red Crescent between 2004 and 2011. The relationship of bloodgroups with wild type K-ras status was also evaluated. Results: Overall distributions of ABO blood groups aswell as Rh factor were comparable between patients (45% A, 7.2% AB, 16.4% B, 31.4% O, and 87.2% Rh+) andcontrols (42.2% A, 7.6% AB, 16.3% B, 33.9% O, and 87.7% Rh+) (p=0.099). However, there were statisticallysignificant difference between patients and controls with respect to O vs. non O blood group (p=0.033) andmarginally significant difference for A vs. non-A blood group (p=0.052). Among patients, the median age was62 (range 17-97), 58.1% were male. There were no statistically significant differences respect to sex and K-rasstatus. Conclusion: In present study, the ABO/Rh blood groups were statistically significantly associated withthe risk of CRC. There were no relationship between K-ras status and ABO blood group and Rh factor. Howeverfurther studies with larger numbers of patients are needed to establish the role of blood groups and to definet he mechanisms by which ABO blood type affect CRC.