Malignant germ cell tumors are an uncommon type of ovarian cancer which account for fewer than 5% of the total in Western countries and 20% in Japan. In females younger than 20, they represent approximately two-thirds of malignant ovarian tumors. Immature teratoma, endodermal sinus tumor, dysgerminoma and mixed type account for the majority (more than 80%), while embryonal carcinoma and polyembryoma are very few. The age of the patients ranges from 6 to 69 years with a median of 16-20 years. Clinically, these tumors are characterized by rapid growth and extensive intraabdominal spread. The symptoms and signs range from 1 day to 6 months with a median of 4 weeks, and the patients usually present with abdominal pain, palpable mass, abdominal distention and vaginal bleeding, and a very few with amenorrhea and precocious puberty. The size of tumors varies from 7 cm to 40 cm with a median of 15-16 cm. The tumor is rarely bilateral (12-19%) and never so in cases of endodermal sinus tumor. Diagnosis depends mainly on age, abdominal symptoms, size and consistency of the tumor, and tumor markers AFP and hCG. Surgery is the first step of management followed by adjuvant therapy, which depends on the histologic type. Dysgerminoma is very sensitive to radiation while other germ cell tumors are not. A combination chemotherapy currently used is VAC or VBP. Both are highly effective. The VBP regimen seems to have a stronger cancerocidal effect, while the VAC regimen is less toxic. VAC produces excellent results in stage I, while VBP is more effective for advanced disease. Conservative surgery and a combination chemotherapy (VAC, VBP) are appropriate for young patients who desire to retain their fertility. Second-look laparotomy is still controversial. As long as AFP or hCG or both can be used to monitor the disease in patients positive for these sensitive and reliable markers, or in an early stage with complete resection, second-look laparotomy is not useful. Survival is associated with prognostic factors, i.e., histologic type, clinical staging operation, lymph node and residual tumor. Patients with endodermal sinus tumor or mixed type tumor had a poorer outcome. The survival rate was higher in patients with earlier disease (stage I or II) and those who underwent primary surgery. Metastasis to the lymph node is not related to prognosis. The presence and size of residual tumors after surgery were closely related to the prognosis.