A 59-year-old male presented with progressive gait and memory disturbance. Computed tomography (CT) showed a huge high density mass, of about 45 mm maximum diameter, in the third ventricle with marked hydrocephalus. Magnetic resonance imaging showed the mass as mixed iso- to hypointensity on T2-weighted imaging and high intensity on T1-weighted imaging. Bifrontal craniotomy was carried out. The histological diagnosis was colloid cyst. Six hours after the operation, a large quantity of cerebrospinal fluid (CSF) was discharged via an epidural drainage, accompanied by generalized convulsion. CT showed multiple brain hemorrhages and subarachnoid hemorrhage remote from the operative field. The cause of hemorrhages is obscure, but postoperative overdrainage of CSF through epidural drainage over a short time following excessive intraoperative CSF aspiration may have contributed to this rare complication.