Purpose: The aim of the study was to examine the clinical presentation, method(s) of treatment, complications, and results in newborns and infants with retroperitoneal germ cell tumors (GCTs). Methods: A retrospective chart review of all patients treated between 1974 and 2002 for GCT located in the retroperitoneumin 2 institutions identified 12 patients with histologically proven retroperitoneal GCT. Vital data concerning pregnancy and delivery were analyzed. Age at diagnosis and symptoms were recorded, as well as possibly associated anomalies. Data concerning surgical treatment, perioperative and postoperative complications, histological staging, and final outcome were all analyzed. Results: In 3 patients, the diagnosis had been made antenatally between 31 and 35 weeks of gestation. In 1 patient, the diagnosis was made at birth, and in 8 later in life (ages 3, 5, 7, 8, 8, 11, 18, and 24 months). Symptoms in these 8 boys and 4 girls were abdominal distension and a palpable upper abdominal mass, right-sided in 5, left-sided in 5, and central in 2; the tumor was usually big. Associated anomalies were noted in 4 patients and were chromosomal in 3 (Down syndrome in 2 and Klinefelter syndrome in 1). One baby died of uncontrollable bleeding during an emergency operation immediately after traumatic birth. The other 11 infants survived. Four other patients showed serious perioperative complications (1 caval vein tear, 1 choledochal tear, 1 cyst rupture, and 1 esophagogastric tear)which were managed without further consequences. Histologically, 4 tumors were mature teratomas, 6 were immature teratomas (grade I in 4, grade II in 1, and grade II-III in 1), and 2 were malignant yolk sac tumors (YSTs). The patients with YSTs underwent surgical biopsy, followed by chemotherapy and excision of the remaining tumor and of the metastases. No adjuvant treatment was administered in the patients with benign disease. Nine survivors with benign tumor are disease-free between 1 and 30 years after surgery. Two patients with YST have now been in remission for 6 and 5 years, respectively. Conclusions: Both this study and the literature review performed testify to the extreme rarity of GCTs in the retroperitoneum. Surgical removal of the tumors appeared to be hazardous because of the extent of the tumor, the displacement and elongation of adjacent structures and organs, and/or the adhesion of the tumor to surrounding tissues; this resulted in several perioperative complications. The long-term results are good, however, with 9 of 10 patients with benign tumors in good health after a mean follow-up of 12 years, and with the 2 patients with YST in remission for 6 and 5 years, respectively. Purpose: The aim of the study was to examine the clinical presentation, method (s) of treatment, complications, and results in newborns and infants with retroperitoneal germ cell tumors (GCTs). Methods: A retrospective chart review of all patients treated between 1974 and 2002 for GCT located in the retroperitoneumin 2 institutions identified 12 patients with histologically proven retroperitoneal GCT. Vital data concerning pregnancy and delivery were analyzed. Age at diagnosis and symptoms were recorded, as well as possibly associated anomalies. Data concerning surgical treatment, perioperative and Results: In 3 patients, the had had made antenatally between 31 and 35 weeks of gestation. In 1 patient, the diagnosis was made at birth, and in 8 later in life (ages 3, 5, 7, 8, 8, 11, 18, and 24 months). Symptoms in these 8 boys and 4 girls were abdominal distension and a palpable upper abdomi nal mass, right-sided in 5, left-sided in 5, and central in 2; the tumor was usually big. Associated anomalies were noted in 4 patients and were chromosomal in 3 (Down syndrome in 2 and Klinefelter syndrome in 1). The other 11 infants survived. Four other patients showed serious perioperative complications (1 caval vein tear, 1 choledochal tear, 1 cyst rupture, and 1 esophagogastric tear) which were managed Histologically, 4 tumors were mature teratomas, 6 were immature teratomas (grade I in 4, grade II in 1, and grade II-III in 1), and 2 were malignant yolk sac tumors (YSTs). The patients with YSTs underwent surgical biopsy, followed by chemotherapy and excision of the remaining tumor and of the metastases. No adjuvant treatment was administered in the patients with benign disease. Nine survivors with benign tumors are disease-free between 1 and 30 years after surgery. Two patients with YST have now been inmission for 6 and 5 years, respectively. Conclusions: Both this study and the literature review performed testify to the extreme rarity of GCTs in the retroperitoneum. Surgical removal of the tumors hazardous because of the extent of the tumor, the displacement and elongation of adjacent structures and organs, and / or the adhesion of the tumor to surrounding tissues; this resulted in several perioperative complications. the long-term results are good, however, with 9 of 10 patients with benign tumors in good health after a mean follow-up of 12 years, and with the 2 patients with YST in remission for 6 and 5 years, respectively.