[Malignant blue nevus].

A 35-year-old male patient suffering from a malignant blue naevus is presented. An uncommon melanocytic naevus and malignant melanoma were considered in the differential diagnosis. The final diagnosis was established by histological examination. Immunohistochemical studies showed a strongly positive reaction of the tumour cells for vimentin and S-100 protein. In addition, tumour cells reacted with the antibody HMB-45.