Clearcell sarcoma is a rare soft tissue sarcoma that displays certain similarities to malignant melanoma. In this paper we describe the karyotypic findings and in vitro growth characteristics of a shorttermcultured clearcell sarcoma. The cultured tumor cells had preserved immunohistochemical characteristics and certain ultrastructural features of the primary tumor, including positivity for vimentin, S-100 protein, and a melanomaassociated antigen, supporting the authenticity of the cultured cells. Cytogenetic analysis revealed an abnormal stemline karyotype of 49,XY, –1, + 8, + 8, + 12, + der(l)t(1;?)(p36.1 –.3;?), t(12,22)(q13;q13). A similar or identical t(12;22) was recently reported in two of four clear-cell sarcomas. It is suggested that the t(12;22)(q13;q13) is a primary cytogenetic abnormality in clear-cell sarcoma and distinguishes this tumor type from malignant melanoma.