We investigated the frequency of gut inflammation and the role of gut lesion in the pathogenesis of the ankylosing spondylitis (AS) in Korean patients. Ileocolonoscopy and biopsy of the colon and terminal ileum were performed on 24 Korean patients with AS. Endoscopic lesions were observed in 7 patients (29.2%). The lesions were found more often in the terminal ileum (6/7) than in the colon (1/7). Histologic signs of gut inflammation were detected in 14 patients (58.3%), acute lesions in 2 patients (8.3%) and chronic lesions in 12 patients (50%). Gut inflammation were as frequently found in Korean patients with AS as in Western patients. These findings suggest that gut inflammation may play a role in the pathogenesis of AS in Korean patients as it does in Western patients.