A malignant mixed gonadal stromal tumor with mesenchymal heterologous elements of the testis is presented. This entity has been described in the ovary, but not hitherto in the testis. Karyotyping and ploidy measurement was done of the primary tumor and of an inguinal and lung metastases. The DNA ploidy and modal chromosome numbers were in agreement with each other in all samples. The most significant cytogenetic finding was the presence of the metacentric germ cell tumor marker i(12p) in an inguinal metastasis. This marker has been demonstrated in testicular and ovarian germ cell tumors and in a mixed Müllerian tumor, which raises the question of a possible relationship between the pluripotency of these tumors and the presence of i(12p).