Synovial sarcoma (SS) is a neoplasm that poses diagnostic problems, due to its histologic heterogeneity. The poorly differentiated variant, in particular, may be histologically indistinguishable from other small round cell tumors. Detection of the synovial sarcoma-associated t(X;18) or SYT-SSX fusion transcripts may be necessary to confirm the diagnosis of SS in difficult cases. Most of SS carry a t(X;18) in about one third of cases as the sole cytogenetic abnormality. We evaluated a case of poorly differentiated synovial sarcoma and their derived tumors in nude mice xenografts and cell cultures. We used a panel of antibodies (including those to intermediate filament, nerve-sheath associated markers, and neuronal and neuroectodermal related antigens) to better establish the immunophenotype, supported by the ultrastructural evaluation. The tumor exhibited the distinctive cytogenetic abnormality t(X;18), together with a der(1)t(1;22)(p36;q12). Present results show that this poorly differentiated synovial sarcoma not only expresses conventional biologic and genetical markers for SS but also neuroectodermal features when transplanted into nude mice and cultured in vitro.