Objective To explore the biological characteristics of mucinous adenocarcinoma deriving from chronic anal fistula and its diagnosis and treatment. Method A retrospective study was made to analyze clinical and pathological features of 4 cases of chronic anal fistula from which mucinous adenocarcinoma developed in our hospital from 1986 to 1997. Results There were three males and one female averaging 50 years old. All patients had chronic history of perianus abscess or anal fistula. This rare mucinous adenocarcinoma originated from the anal fistula and the associated anal glands. The canceration of anal fistula was due to chronic inflammation and scarring. The definitive diagnosis of the carcinoma depends on biopsy of the fistula and the related tumor. Metastasis to groin lymph nodes was found in two patients. Three cases underwent Miles operation with chemotherapy; two of the three patients also had resection of groin lymph nodes. Three patients survived more than five years. One patient treated only with chemotherapy died three months later. [WT5”HZ] Conclusion [WT5”BZ] Mucinous adenocarcinoma following chronic anal fistula is less malignant and has better prognosis compared to primary rectal and anal mucinous adenocarcinoma.