Purpose: Colorectum diversion with a proximal stoma is often the preferred surgical approach in patients with Crohn's disease-related anorectal lesions or refractory colitis. To date, few studies have assessed the incidence and prognosis of cancer in the diverted anorectal segments. This study aimed to evaluate the clinical characteristics and prognosis of anorectal cancer associated with Crohn's disease following fecal diversion.Methods: This was a retrospective study based on medical records of patients diagnosed with Crohn's disease between 1999 and 2020. It was conducted at Yokohama Municipal Citizen's Hospital. Patients diagnosed with anorectal cancer following fecal diversion were identified, and their prognosis was the primary outcome measure.Results: Among 1,615 patients, 232 patients (14%) underwent colorectum diversion. Of those 232 patients, 12 were diagnosed with anorectal cancer following fecal diversion, nine were diagnosed with advanced cancer, 10 underwent abdominoperineal resection, and eight died. The overall five-year survival rate in patients diagnosed with anorectal cancer following fecal diversion was 20%. Conclusion: Crohn's disease-associated anorectal cancer following fecal diversion was challenging to diagnose early, and patients had a poor prognosis even after curative resection. Early abdominoperineal resection may be considered for patients with Crohn's disease who cannot benefit from cancer screening and surveillance due to difficulty accessing the anorectal stricture via endoscopy.