Objective: Anorectal malignant melanoma(AMM) is a rare and aggressive malignant tumor,and its treatment still controversial.This study was to investigate and summarize our experience on diagnosis,treatment and misdiagnosis of AMM.Methods: From August 1980 to December 2009,42 patients with AMM were treated in our hospital.The clinical data of those patients were retrospectively analyzed,including the major symptoms,treatment and prognosis.Further immunophenotyping analyses using antibodies to S-100 protein,HMB-45 reactive antigen and vimentin were performed in 22 specimens.Results: The major complaints among the 42 cases were hematochezia(23/42,55.0%),anal masses(12/42,28.6%),changes in stool character(4/42,9.5%),and anal tenesmus or pain(3/42,7.1%).The misdiagnosis rate was 62%(26/42),the most common misdiagnosis consisted of hemorrhoid(9/26,34.6%),polyps(11/26,42.3%) and rectal cancer(6/26,23.1%).28 cases underwent abdominoperineal resection,10 underwent local wide excision,3 underwent palliative operation,and 1 with no operation.After surgery,15 patients underwent radiotherapy,21 underwent chemotherapy and 8 were treated with both.22 cases deceased within 1 year,11 within 2 years,5 within 3 years and 1 within 4 years.The median survival time was 11 months,with the longest of 45 months.The stained in 19 of 22(86.4%) and vimentin in 21 of 22(95.5%).Conclusion: AMM is a rare disease with a poor prognosis and with an aptitude of being misdiagnosed.Hematochezia is the most common symptom.Immunohistochemical staining is conducive to the diagnosis of AMM.Operation is the major treatment,the operation type should be individualized.