Colloid cysts are rare benign tumors of the third ventricle with diverse clinical presentation, which vary from incidentally found cysts to acute death. An uncommon hemorrhage in these cysts is a life threatening complication which can cause obstructive hydrocephalus with acute deterioration of the patient and sudden death. We present a case of 35-year-old man with large hemorrhagic colloid cyst of a third ventricle causing acute obstructive hydrocephalus even though magnetic resonance image with low T2 signal of the cyst suggested its clinically stable nature. Only 3 cases of in vivo diagnosed hemorrhagic colloid cysts have been reported in the literature.