A 35-year-old woman, gravida 1, para 1, underwent cesarean section in her 39th week of pregnancy. At the time of operation, multiple retroperitoneal tumors were found. Postoperative computed tomography and magnetic resonance imaging showed multiple solid tumors, each approximately 3-5 cm, in the right pelvic retroperitoneal space. Total resection of the tumors was performed without any macroscopic residual. A systematic workup for the primary tumor from which the retroperitoneal tumors may have metastasized failed to demonstrate any responsible tumor. We therefore assumed it to be a primary retroperitoneal tumor. The histopathologic features of the tumors were consistent with small-cell carcinoma. Two months postoperatively, recurrent tumors in the right inguinal and common iliac regions were detected. Since chemotherapy with irinotecan hydrochloride or paclitaxel did not produce any beneficial effect, a second tumor reduction surgery was performed 8 months after the initial operation. Four months after the second operation, a third operation including total hysterectomy, bilateral salpingo-oophorectomy, and tumor resection in the contralateral iliac region were done. Afterward, a new recurrent tumor appeared along the aorta up to the left supraclavicular node. The patient died 19 months after the first operation.