We report two cases of cutaneous malignant peripheral nerve sheath tumors. One occurred in a patient without neurofibromatosis and manifested as a recurrent scalp nodule. Histologically, the lesion began as a benign-appearing, dermal neurofibroma and progressed to a highly cellular, pleomorphic neoplasm with prominent mitotic activity and invasion of the subcutis. Immunohistochemical and ultrastructural examination confirmed the nerve sheath origin of this tumor. The other case presented as a large scalp mass in a patient with an established diagnosis of neurofibromatosis; its immunohistochemical characteristics were identical to those of case 1. Although malignant peripheral nerve sheath tumors are uncommon in the skin, they can be effectively separated from other spindle cell neoplasms by specialized pathologic studies.