BACKGROUND: Enterotoxigenic Bacteroides fragilis (ETBF) is an enterotoxin-producing bacterium that possibily has a role in the occurrence and progression of colorectal cancer (CRC) by modulating the mucosal immune response and inducing epithelial cell changes. The aim of this study was to investigate the frequency of ETBF in stool samples of CRC patients and healthy volunteers. METHODS: A total of 60 stool samples from confirmed CRC patients and 60 stool samples from healthy volunteers with no personal or familial history or diagnosis of colorectal disease were collected. Stool samples were screened for direct detection of B. fragilis using PCR targeting the marker genes of neu and bft. Enterotoxin isotypes bft-1, bft-2 and bft-3 were also detected in B. fragilis positive samples. RESULTS: The frequency of B. fragilis among CRC and control cases was 58.3 and 26.6%, respectively (P < 0.05). The rate of bft gene in CRC cases was significantly higher than in controls (P < 0.05). Also, the presence of bft gene in CRC patients stage III was significantly higher than stages I and II (P < 0.05). Enterotoxin isotype bft-2 was detected with higher frequency among CRC patients than healthy control (P < 0.05). CONCLUSION: Our results show the association between fecal ETBF and CRC, and we suggest that detection of ETBF may be a potential marker for colorectal cancer diagnosis. However, additional investigations on tumor and paired normal tissue samples are required to substantiate this possible correlation.