The study was undertaken to assess the ventricular system of the brain in normal korean adults on the base ofCT. The computerized tomographic examinations of 334 Korean adults between ages of 15 to 50 years, performed atSeoul National University Hospital, were evaluated. The known to be a reliable indicator of the ventricular size.This ratio was measured at the level of the lateral, third and fourth ventricles respelctively. The shape of thequardigeminal and suprasellar cistern was analyzed. The resuls are as follows; 1. The cerebroventricular ratios ofthe lateral ventricle at the level of the widest bifrontal and bicaudate diameters were 0.30±0.04 and 0.14±0.02,respectively. The lateral ventricle was asymmetric in 12.6%, of which the left side was usually larger than theright. 2.There was correlation between the cerebroventricular ratio and age, i,e., with increase of age, the C-Vratio increased slightly. 3. The cerebroventricular ratio of the third ventricle was 0.03±0.01. 4. Thecerebroventricular ratio of the fourth ventricle in width and height was 0.14±0.02 and 0.10±0.03, respectively.The anteroposterior position index of the fourth ventricle was 0.42±0.04. 5. The quadrigeminal cistern showedU-shape in 23.4%. 6. The suprasellar cistern showed pentagonal shape in 61.1%, round in 28.4% and hexagonal in10.5%. 7. There was no significant difference between male and female according to the above results.