A case of intracranial mixed malignant germ cell tumor (GCT) in a patient with the Klinefelter syndrome (KS) is reported. Extragonadal GCTs, including those of intracranial origin, have previously been noted in KS patients. A review of the English literature suggests that although this phenomenon is rare, there appears to be more than a coincidental relationship between GCTs and a 47, XXY karyotype. This case represents the sixth reported case of intracranial GCT in KS but the first to be histologically confirmed to have mixed malignant germ cell elements. This occurrence of malignant cell types in a KS patient emphasizes the need for a histologic diagnosis prior to initiation of therapy.