Anorectal malignant melanoma is a rare disease and has a uniformly poor prognosis. The following are two reported cases from Buddhachinaraj Hospital. A 55-year-old and a 65-year-old female patients presented with rectal bleeding. Large anorectal masses with regional lymph node involvement were detected
initially. They exhibited different histological features which were atypical round cell resembling lymphocytes or were small cell appearance and spindle cell appearance similar to sarcoma. The diagnosis was confirmed by expression of S100 protein and HMB45. Abdominoperineal resection (APR) was the treatment
of choice in both patients. The former case died in the fourth month after diagnosis because of distance metastasis and congestive heart failure. The latter case is receiving postoperative adjuvant therapy.

Keywords: Anorectal malignant melanoma, Histological features, Abdominoperineal resection (APR)