A previously healthy 31-year-old Japanese man presented with a very rare germinoma of the corpus callosum without other intracranial lesions manifesting as transitory speech disturbance. Magnetic resonance (MR) imaging revealed a heterogeneously enhanced mass in the corpus callosum extending into the cavity of the septum pellucidum. A tumor specimen obtained by stereotactic biopsy revealed a two-cell pattern germinoma containing human chorionic gonadotropin (HCG)-beta-positive giant cells. The cerebrospinal fluid and serum levels of HCG and HCG-beta subunit were measurable. The diagnosis was germinoma with syncytiotrophoblastic giant cells. Three cycles of chemotherapy consisting of ifosfamide, cisplatin, and etoposide, followed by radiation therapy achieved complete remission, and 5 cycles of chemotherapy with carboplatin and etoposide were added. MR imaging performed 40 months after the diagnosis showed a cicatricial cyst in the body of the corpus callosum, the original tumor site. All 11 previously reported cases of germinoma in the corpus callosum were associated with synchronous or metachronous intracranial lesions. These patients tended to be older than patients with general intracranial germinoma. Germinoma should be included in the differential diagnosis of corpus callosum tumors, especially in young adult males.