Twenty cases of melanotic neuroectodermal tumor of infancy (MNTI) are reported. The patients (13 females, seven males), whose ages ranged from 1 to 9 months (mean, 5 months), typically presented with a rapidly growing mass. Tumor sites included the maxilla (13 cases), mandible (three cases), dura (two cases), brain (one case), and skull/orbit (one case). The mean tumor size was 3.5 cm (range, 1.0-10.0 cm). Follow-up was obtained on 12 cases. Five tumors (45%) recurred within 4 months of diagnosis, but none metastasized. One surgical death occurred. Histologic appearance was distinctive, with tubular or alveolar formations of large melanin-containing cells around nests of smaller neuroblastic cells possessing scant or fibrillar cytoplasm. Twelve tumors were studied immunohistochemically; tumor was positive for cytokeratin in 12 of 12, for HMB 45 in 12 of 12, for vimentin in seven of eight, and for epithelial membrane antigen (EMA) in four of nine tumors, mainly in the large cells. Neuron-specific enolase (NSE) (seven of 12) and Leu 7 (nine of 12) were positive in small and large cells; some tumors also expressed synaptophysin (four of 12), glial fibrillary acidic protein (GFAP, three of 12 tumors), or S-100 protein (two of 12 tumors). No staining was found for chromogranin, desmin, or carcinoembryonic antigen (CEA). Eight of 10 tumors studied had interpretable results on flow cytometry (FCM) (four DNA diploid, three DNA aneuploid, and one DNA diploid with a prominent shoulder). Tumor recurred locally in two of five cases with follow-up, and we were unable to demonstrate the usefulness of FCM in predicting recurrences. Further studies are necessary to define better the potential usefulness of FCM in predicting aggressive behavior. Distinctive morphology and multiphenotypic (epithelial, neural, melanocytic) expression distinguish MNTI from melanoma and metastatic neuroblastoma.