PURPOSE: To determine the characteristic MR imaging findings of pineal germinoma, and differential diagnosisfrom other germ cell tumors. MATERIALS AND METHODS: MR images of patients with histopathologically proven pinealgerminoma(n=14) and other pineal germ cell tumors(n=10) were retrospectively analyzed with regard to size, signalintensity and homogenetiy, enhancing features, cyst formation, and multiplicity of lesions. Other pineal germ celltumors were the mixed germ cell tumors (n=4), malignant teratomas(n=3), choriocarcinoma(n=1), embryonalcarcinoma(n=1), and endodermal sinus tumor(n=1). Tumor markers were evaluated. RESULTS: On T1-weighted images,germinomas showed homogeneous(86%) or iso signal intensity(93%), while other germ cell tumors showedinhomogeneous(70%) or iso signal intensity(70%). On T2-weighted images, germinomas showed homogeneous(64%) or isosignal intensity(57%), while other germ cell tumors showed inhomogeneous(70%) or high signal intensity(80%). OnGd-DTPA enhanced images, germinomas showed homogeneous (93%) or strong enhancement(64%), while other germ celltumors showed homogeneous(60%) or strong enhancemant(70%). Cyst formation was noted in ten patients(71%) withgerminoma and in six(60%) with other germ cell tumors, Invasion of surrounding structures was seen in 11 patients(79%) with germinoma and in five(50%) with other germ cell tumors. Lesions were multiple in three patients(21%)with germinoma. Thirteen of 14 patients with germinoma had normal serum alpha-FP(tetoprotein) and beta-HCG(humanchononic gonafotrophin) levels. Two of four patients with mixed germ cell tumors had elevated serum alpha-FP andalpha-HCG levels; in the other two, elevated serum alpha-FP or beta-HCG levels were noted. In the malignant teratoma andembryonal carcinoma patients, serum alpha-FP and beta-HCG levels were normal. The patient with choriocarcinoma had anelevated serum beta-HCG level. CONCLUSION: On T1W1, the only significant differential point(P<0.01) betweengerminomas and other germ cell tumors was homogeneity. Germinomas were frequently homogeneous, and iso signalintensity on T1WI and T2WI, strong enhancement, and the formation of small cysts(<3mm) was noted. This MR imagingfinding, combined with assay for tumor markers, is helpful for the differential diagnosis of pineal germinoma andother cell tumors.