A well-documented case of malignant blue nevus is presented, along with an in-depth review of the literature. Malignant blue nevus is a rare form of malignant melanoma. A cellular blue nevus is the precursor lesion. The scalp is the most common site. The tumor often presents clinically as a progressively enlarging or multinodular blue-black lesion. The histologic pattern is fascicular dense collections of pigmented, pleomorphic spindle cells. Because of marked regional histologic variation within a malignant blue nevus, however, sampling error can cause delay in recognition of malignancy. A high clinical index of suspicion and appropriate biopsy technique are necessary to reach an early diagnosis. The most common site of metastasis of a malignant blue nevus is the lymph node. The phenomenon of benign lymph node nevus cell metastasis, which may occur with benign blue nevi, must be differentiated from a true malignant metastasis of a malignant blue nevus.