A 19-year-old female presented with an unusual glial cyst of the thalamus that caused development of acute hydrocephalus due to hemorrhage and manifested as headache and fainting attacks. Computed tomography showed a large cystic mass lesion in the left thalamus with intracystic hemorrhage. The cyst was subtotally removed. Microscopic examination revealed mild gliosis with marked hemosiderin deposits. The inner surface of the cystic wall lacked an epithelial lining. The diagnosis was glial cyst. Magnetic resonance (MR) imaging 2 months after surgery showed a residual cyst in the left thalamus. However, after 12 months she was asymptomatic, neurologically intact, and MR imaging showed no regrowth of the cyst. Treatment of glial cyst must provide sufficient communication between the cyst and the cerebral ventricles rather than attempt total removal of the cyst, which may present a considerable challenge.