AIM: Ulcerative colitis (UC) is a known contributor to the development of colitis-associated cancer (CAC), although the exact mechanism remains to be elucidated. CAC typically presents as a flat type macroscopically and manifests histologically as mucinous carcinoma and signet ring cell carcinoma. While the relationship between disease duration and chronic inflammation has been studied, the impact of disease duration on CAC outcomes has yet to be thoroughly investigated. The aim of this study is to examine the effect of UC duration on the clinicopathological features of CAC. METHOD: This study analysed data from the Japan Society for Colorectal Cancer Research involving UC patients diagnosed with colorectal cancer. The sample consisted of 1200 patients, and their histological and clinicopathological features were analysed. Cutoff values were established at 5 and 15 years for comparisons. Trends and prognostic outcomes corresponding to disease duration were evaluated. RESULTS: Comparison between two groups (disease duration 0-5 and >5 years) revealed a significant correlation in terms of diagnostic opportunity, vascular invasion, N factor, pathological stage and tumour location. However, between the two groups of 0-15 and >15 years, a significant correlation was identified only in diagnostic opportunity, the presence of primary sclerosing cholangitis. Trend analysis of disease duration showed significant correlations between diagnostic opportunity, histological type, vascular invasion and tumour location, with no significant differences observed in prognostic outcomes. CONCLUSION: Our analysis highlighted distinct histological and clinical features in the short-term and long-term disease groups, and these features appear to intensify with increased disease duration. Since no significant difference in prognosis was found, there may not be a need to distinguish between them in cancer treatment.