The study was undertaken to assess the ventricular system of the brain in normal Korean adults between ages of 15 to 50 years, performed at Seoul National university Hospital, were evaluated . The crebro-or cerebello-ventricular ratio, between ventricular size and brain parenchyme width, has been known to be a reliable indicator of the ventricular size. The ratio was measured at the level of the lateral, third and fourth ventricles respectively. The shape of the quardigeminal and suprasellar cistern was analyzed. The results are as follows : 1. The cerebroventricular ratios of the lateral ventericule at the level of the widest bifrontal and bicaudate diameters ere 0.30${pm}$0.04 and 0.14${pm}$0.02 , respectively. 2. There was correlation between the cerebroventrivular ratio and age, i.e. with increase of age, the C-V ratio in reased slightly. 3. The cerebroventricular ratio of the third ventricle was 0.03${pm}$0.01. 4.The cerebroventricular ratio of the fourth ventricule in width and height was 0.14${pm}$0.02 and 0.10 ${pm}$0.03. respectively. 5. The quadrigeminal cistern showed W-shape in 76.7% and U-shape in 23.4%. 6. The suprasellar cistern showed pentgonal shape in 61.1% round in 28.4% and hexagonal in 10.5%. 7. There was no significant difference between male and female according to the above results.