Background: Growing teratoma syndrome (GTS) is an infrequent clinical phenomenon. GTS is defined as an enlarging metastatic mass during systemic chemotherapy for advanced nonseminomatous germ cell tumors (NSGCT) despite decreasing serum tumor markers. Complete surgical resection of the mass is mandatory to achieve a favourable outcome. We report on our single center experience in the management of GTS. Methods: Between January 2000 and August 2009 postchemotherapeutic retroperitoneal lymph node dissection (PCRPLND) was performed in 162 patients (pts) with advanced NSGCT. Fourteen pts (4.9%) fulfilled the criteria of a GTS: enlarging metastatic mass in the retroperitoneum or visceral organs during systemic chemotherapy with normalized or regredient tumor markers. In all cases of GTS a complete radical bilateral PCRPLND including the resection of adjacent visceral and vascular structures was performed. Results: Median patient age was 24.5 (18 to 52) years. All patients exhibited NSGCT with a good or intermediate prognosis according to IGCCCG; in all cases the primary tumor contained predominantly (greater than 50%) mature teratoma; 10 and 4 patients presented with clinical stage IIC and III, resp. Median tumor diameter at time of surgery was 6,5 (3,0-35)cm. Tumor markers were normalized in 12 out of 14 patients and markers plateauted in 2 out of 14 patients. Tumor masses were localized in the retroperitoneum in 12 pts.; two patients had additional pulmonary metastases which were resected in a second approach. Median time from start of chemotherapy to surgery was 4.8 (1.5 to 26.5) months Median surgical time was 265 (165 to 585) minutes, and median blood loss 650 (450 to 2,000) ml. Four pts required resection of the inferior vena cava or abdominal aorta with implantation of a prosthetic graft; adjunctive nephrectomy was performed in three pts. After a median follow-up of 4.2 years two pts developed recurrent disease; the remainder are alive without evidence of disease. Conclusions: GTS is a rare phenomenom among pts with advanced NSGCT and necessitates complete surgical resection of all masses with curative intention. Surgery should be considered at time of progression to facilitate complete removal of the mass. Due to the complex surgery, treatment should be performed at specialized centers.