A 47-year-old woman had a lesion of the uterine cervix that presented clinically as a protruding or aborted leiomyoma. Grossly the tumor occupied a substantial portion of the cervical and endocervical region. Histologically it showed a spindle cell neoplasm arranged in large fascicles that penetrated deeply into the fibromuscular wall of the cervix. The tumor cells had abundant pink cytoplasm that contained considerable brown melanin granules confirmed by Fontana's stain. Cytologically nuclear pleomorphism, hyperchromatism, and giant nuclear forms were observed. Mitoses were also seen. Localized nuclear palisading was present. Electron microscopic examination of paraffin-embedded material revealed numerous premelanosomes and opaque granules that were compatible with mature melanosomes, thus confirming melanogenesis in the tumor. Tumor cells exhibited focal projections, and the connective tissue showed abnormal spacing of collagen. Basal lamina material was noted focally on tumor cell surfaces. Immunocytochemistry showed a positive reaction to S-100 protein and HMB-45 in tumor cell cytoplasm.