OBJECTIVE To determine the value of delayed surgical resection in patients with central nervous system germ cell tumors who exhibit less than complete radiographic response despite declining serum and cerebrospinal fluid (CSF) tumor markers after initial chemotherapy. METHODS We retrospectively analyzed 126 patients enrolled on two international multicenter clinical trials (the First and Second International Central Nervous System Germ Cell Tumor Studies) for patients with newly diagnosed central nervous system germ cell tumors. After at least three cycles of chemotherapy, 10 of these patients underwent delayed surgical resection owing to evidence of residual radiographic abnormalities despite declining or completely normalized serum and CSF levels of alpha-fetoprotein and human chorionic gonadotropin. RESULTS Eight of these patients demonstrated nongerminomatous germ cell tumor elements at the time of initial diagnosis. In these patients, either serum or CSF tumor markers were elevated initially. Two patients demonstrated pure germinomas with normal levels of serum and CSF tumor markers. After chemotherapy, radiographic evaluation revealed a partial response in seven patients, a minor response in one patient, and stable disease in two patients. All 10 patients had either normal or decreasing levels of serum and CSF tumor markers before second-look surgery. At delayed surgical resection, 7 of the 10 patients underwent gross total resection, and 3 patients underwent subtotal resection of residual lesions. Pathological findings at second-look surgery demonstrated three patients to have mature teratomas, two with immature teratomas, and five with necrotic or scar tissue alone. To date, 7 of the 10 patients have had no recurrence during an average follow-up time of 36.9 months (range, 3-96 mo). Three of four patients with nongerminomatous germ cell tumors who had tumor markers that were decreased, but not normalized, before second-look surgery eventually developed tumor dissemination/progression, and they required subsequent radiation therapy despite having teratoma or necrosis/scar tissue at delayed surgery. In contrast, three of four patients with nongerminomatous germ cell tumors and completely normalized markers did not progress and did not require radiation therapy. CONCLUSIONS Delayed surgical resection should be considered in patients with central nervous system germ cell tumors who have residual radiographic abnormalities and normalized tumor markers, because these lesions are likely to be teratoma or necrosis/scar tissue. However, second-look surgery should be avoided in patients whose tumor markers have not normalized completely.