A three year old, male, castrated Doberman pinscher presented for progressive signs of inappetance, lethargy, and enophthalmos. On neurological and physical examination, the significant findings included profound obtundation, anisocoria, abnormal physiologic nystagmus, and bradycardia. The neuroanatomic diagnosis was the diencephalon and the cranial nerves ventral to it. The signalment and clinical signs suggested a diagnosis of a germ cell neoplasm. This was subsequently confirmed on necropsy. Primary intracranial germ cell neoplasms are rare tumors that have been described in various species including the dog. Variable theories have been suggested to explain how they occur in this location. Affected dogs range in age from 3-5 years old, and the Doberman pinscher breed is overrepresented. The tumor is usually a large mass located on the ventral aspect of the diencephalon. On gross examination the mass usually contains multiple necrotic and mineralized regions. Three main types of cells have been described histologically: variable sheets of cells resembling seminomas or dysgerminomas; cuboidal to columnar, epithelial-like cells forming secretory glandular structures; and vacuolated hepatoid cells. These characteristics help distinguish this tumor from other potential differential diagnoses. Occasionally, these cells will stain positive for a tumor marker, alpha feto-protein. This neoplasm has various treatment options in human medicine including surgery, radiation therapy and chemotherapy with good long term results.