Five cases of spermatocytic seminoma of the testis associated with a sarcomatous component, one of them of rhabdomyosarcomatous type, are presented. No recognizable teratomatous structures were identified in any of the cases. The presence of the sarcomatous elements transformed the usually innocuous spermatocytic seminoma into a highly aggressive neoplasm, which led to the patients' death in at least two cases. The sarcomatous elements may represent a nonseminomatous germ cell component, but we prefer to view them as an expression of anaplastic transformation of the tumors, analogous to that seen in tumors in other organs.