Extragonadal germ cell tumors (EGCT) represent only 2-5% of adult germ cell malignancies. Some publications from Asia have reported inferior treatment outcomes compared to data from an international study group. To ascertain whether this is generally the case, here we analyze treatment outcomes for 30 Japanese patients with EGCT. The medical records of 30 patients (25 nonseminomas and 4 pure seminomas) treated from 1992 to 2002 were reviewed retrospectively. All patients with seminoma achieved long survival except one who died of chemotherapy-related sepsis. Ten and 11 patients with EGCT presented with mediastinal and retroperitoneal primary sites, respectively. The 5-year overall survival (OS) and progression-free survival (PFS) for nonseminoma was 71% and 42%, respectively. The 5-year OS and PFS was 60% and 44%, respectively, for 10 patients with mediastinal nonseminoma, and 91% and 48%, respectively, for patients with retroperitoneal nonseminoma. Tumor marker values on day 7 were available for 19 patients. Among the 19 patients in whom AFP or beta-HCG were measured on day 7, the values had declined in 12 patients and were transiently elevated in 7 patients compared to pretreatment values. The transient elevations of tumor markers were significantly associated with poor OS (P = 0.02) and PFS (P = 0.008). The treatment outcome of Japanese patients with EGCT seemed to be comparable to that reported from international studies, suggesting no difference between ethnic groups. Transient tumor marker elevations on day 7 predict poor survival in EGCT patients and may be a useful parameter for identifying patients requiring more aggressive treatment.