The authors describe a 14-year-old girl with small round cell tumor originating in the chest wall analyzed by the extensive studies including light and electron microscopic examination, histochemical study, immunochemical study, cytogenetics, and gene analysis. A cell line producing carcinoembryonic antigen (CEA) and neuron-specific enolase (NSE) has been established from pleural effusion of the pulmonary metastatic tumor. Cytogenetic analysis disclosed a reciprocal translocation (11;22)(q24;q12). Additionally, immunocytochemical studies demonstrated that CEA, NSE, vimentin, cytokeratin, and epithelial membrane antigens are positive, but desmin and S-100 protein are negative. Although neurofilament was negative in the pulmonary metastatic tumor cells, it became positive in cell line in vitro. These results suggest that this tumor may be derived from the primitive and pluripotential cells, differentiating into mesenchymal, epithelial, and neural features in variable proportions.