Growing teratoma syndrome is a rare condition among patients with nonseminomatous germ cell tumors who present with enlarging metastatic masses during appropriate systemic chemotherapy and normalized serum markers. Retroperitoneal residual masses are a common finding after chemotherapy for the nonseminomatous tumors of the testis. These might contain mature teratoma, fibrotic tissue, or tumor. Mature teratoma, which is unresponsive to chemotherapy, might result from evolution of a malignant lesion during treatment or it might represent a metastasis from a focus of mature teratoma in the primary testicular tumor. This article reviews a case of a growing teratoma syndrome.