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The term "growing teratoma syndrome (GTS)" has been used as follows: patients with germ cell tumor (GCT) who present with enlarging original/metastatic masses during or after appropriate systemic chemotherapy despite normalized serum markers. In other words, the definition of the term GTS is not fully established. We analyzed and reviewed our case series regarding GTS that developed after the treatment of central nervous system (CNS) nongerminoatous germ cell tumors (NGGCTs). Our institutional review board approved this retrospective study. Between 2003 and 2018, we treated 16 patients (16 males; age ranging from 5.4 to 51.9 years, median 13.8) with CNS-NGGCT at our institution. We reviewed those patients and also reviewed the literature about GTS of CNS. We defined primary GTS (p-GTS) as the enlargement of cyst size and/or solid tumor occurred during treatment in the absence of marker elevation, and recurrent GTS (r-GTS) as the enlargement of teratoma after complete response of initial tumors. Among 16 patients with CNS-NGGCT, we surgically confirmed mature/immature teratoma components in 15 patients. Two patients underwent surgical removal of tumor before neoadjuvant therapy, and among the rest 14 patients, 6 developed p-GTS, and 2 patients underwent salvage surgery during chemo-/chemoradiotherapy. Those with histologic diagnosis of immature teratoma during salvage surgery had a shorter interval from the initiation of chemoradiotherapy compared with mature teratoma (P < 0.05). One patient developed r-GTS. In the literature review, most of the p-GTS consisted of enlargement with the multicystic component. Histologic diagnosis of immature teratoma during salvage surgery was observed in earlier stages of chemoradiotherapy (P < 0.05, log-rank test). Previous history of p-GTS might be a risk factor of r-GTS. The incidence of p-GTS, enlargement of the cystic component during treatment, is not rare. Physicians need to be aware of this important phenomenon. [ABSTRACT FROM AUTHOR]