BACKGROUND Data on frequency distribution of ABO-Rh blood groups in cardiac syndrome X (CSX) patients are not available. We aimed to investigate the distribution of ABO-Rh blood groups in these patients. METHODS A total of 247 CSX patients' records were reviewed in a cross-sectional study from 2006 to 2010. One hundred forty six patients (59.1%) were female, and the mean patient age was 52 ± 11 years. The frequency of ABO-Rh blood groups was compared to the frequency of these blood groups in the West-Azerbaijan province, Iran; general population. RESULTS Blood groups distribution among CSX patients showed phenotypes A, B, AB, O and Rh negative as 33.1%, 21.9%, 9.3%, 35.8%, and 7.9%, respectively. According to our results, there were no differences in ABO-Rh blood groups distribution between CSX patients and normal population. CONCLUSIONS These data suggest that ABO-Rh blood groups might be unassociated with CSX.