The growing teratoma syndrome (GTS) is defined as a detection of an enlarged mass during or after chemotherapy treatment for germ cell tumor. We report a case of an 18-year-old girl treated for growing teratoma syndrome after chemotherapy for malignant germ cell tumor of the ovary associated with peritoneal gliomatosis. Chemotherapy induced normalisation of alpha-fetoprotein rate whereas there was an enlargement of the mass. Subsequent complete resection was performed, and the patient remained in good control for 60 months. This clinical picture suggested the diagnosis of "GTS". This syndrome can lead to confusion with progression or relapse of a germ cell tumour because of increase in tumour volume during chemotherapy, so it is important to recognize it.