Colloid cysts of the third ventricle are benign tumors that may cause brief, severe headache and, rarely, death. We present a patient with frequent, episodic, brief, severe headaches of 2 weeks' duration who suddenly became obtunded. We reviewed the literature on the symptomatology of colloid cysts and conclude that any patient with less than a 1-year history suggestive of a third ventricular colloid cyst causing brief, severe headaches should be aggressively investigated.