Aneurysm of the vein of Galen is a very rare disease. The authors present a case of secondary aneurysm of the vein of Galen which was confirmed by characteristic clinical symptoms, brain CT and angiographic findings. The patient was a 14-year-old right handed girl with intermittent headache, nausea, vomiting, dysphasia and gait disturbance. Neurologic examination revealed dysarthria, nasal voice, blurring of both margins of optic discs, truncal ataxia and dysdiadochokinesia. Sensory function was normal but right hemiparesis was seen. Roentgenogram of the skull revealed diffuse thinning of the calvarium, widening of sella turcica and erosion of clinoid processes. Computed tomogram of the brain showed dilatation of all ventricles and round hyperdense mass behind the third ventricle in the midline. The lesion was enhanced markedly and homogeneously. Left and right internal carotid angiograms showed arteriovenousmal-formation with drainage to the aneurysm of the vein of Galen.