Three patients with malignant blue nevus are reported-one on the right side of the body, one on the right arm, and one on the face. The criteria and difficulty of histopathological diagnosis are considered as well as the differential diagnoses for this tumor. The therapy is described, and the possible relations between malignant blue nevus and certain other tumors (e.g., atypical or locally aggressive cellular blue nevus) are explored. A review of the literature reveals that there is current disagreement about the exact prognosis for these tumors and indicates the need to collect data for all patients observed.