Anal canal duplications are very rare noncommunicating second anal orifices located posterior to the true anus. In this study, 5 adult cases of anal canal duplication are reported as extremely rare entities in the literature. The medical records of anal canal duplication patients treated from 2011 to 2014 were reviewed retrospectively. Five adult patients with symptoms of mucous discharge, anal pain, and or perianal fistula/abscess were admitted. Findings of physical examination and radiologic imaging (pelvic magnetic resonance, endoanal ultrasound, and or colonoscopy) suggested anal canal duplication. The mean age of patients was 40.4 +/- 8.7 (range, 33-55), and the mean follow-up period was 18.4 +/- 11.2 (range, 6-36) months. Histologic features of the removed samples confirmed anal canal duplication. All patients underwent complete surgical excision of the rudimentary anal canal. Anal canal duplication is a very rare congenital anomaly, and 5 additional adult cases are reported. Although this is a referral center, the recent accumulation of 5 adult cases of anal canal duplication suggests that this malformation might be more prevalent and frequently overlooked.