We describe a case of malignant melanoma, which appeared on the plaque of multiple congenital melanocytic nevuses (CMN) . A 33-year-old woman had a huge plaque of multiple CMN on her back at birth. The plaque was composed of numerous, brown to black, up to 2cm in size, papules or macules intermingling with normal skin. One of the black nodules had been gradually enlarged with occasional bleeding. The lesion was clinically and histologically diagnosed as malignant melanoma. Wide excision was performed in association with chemotherapy. After operation no reccur-ence has been noted.
