BACKGROUND/AIMS: In addition to the inhibition of cyclooxygenase-2, the chemopreventive effect of non-steroidal anti-inflammatory drugs on the nuclear translocation of beta-catenin has been suggested in patients with familial adenoma polyposis. We investigated the effect of aspirin on the beta-catenin signaling pathway in patients with sporadic colorectal adenoma. METHODS: We selected patients diagnosed with colorectal adenoma. Patients who had been taking aspirin for more than 12 months were identified as the aspirin group, and those who did not were the non-aspirin group. Their characteristics, including size and degree of dysplasia, were compared. Immunohistochemical staining was conducted and the expression levels of nuclear beta-catenin and cyclin D1 were investigated. RESULTS: The median duration of aspirin intake was 37 months; there were no significant differences in the size, histological type, and degree of dysplasia between the two groups. Nuclear beta-catenin expression was observed in 43.2% of the patients in the aspirin group and in 18.9% of those in the non-aspirin group (P < 0.05). There was no significant difference in nuclear cyclin D1 staining between the aspirin (78.4%) and non-aspirin (91.9%) groups. CONCLUSIONS: In this retrospective study, nuclear beta-catenin expression in sporadic colorectal adenoma in the aspirin group was not inhibited compared with that in the non-aspirin group. Therefore, further prospective studies with a large number of patients are necessary.