: Objectives: To detect average dimensions and indices of normal brain cerebral hemispheres and fourth ventricles in relation to age and gender.Subjects & Methods: 135 subjects; 70 males (M) and 65 females (F) were categorized into 4 age groups (G): MG1 & FG1 included subjects 60 years old. CT imaging was conducted according to Agapejev; using high resolution scanner for measuring the fourth ventricle; the fourth ventricular anteroposterior diameter (AP), laterolateral diameter and fourth ventricular indices.Results: As regard the measured parameter of the fourth ventricle, the anteroposterior diameter (AP) and the laterolateral diameter (LL) showed a significant increase after the age of forty in both sexes. The indices of the fourth ventricle (AP/CR) and (AP/ff) showed no significant changes with age and sex but these indices had some degree of changes during human life time. On the other hand the only index that does not suffer influence of age and sex at all, it was (AP/LL) index. Considering the sex difference in ventricular dilatation in the present work, AP/LL was the only parameters which showed no difference between males and females so considered as (sentinel index of the fourth ventricle).Conclusion: The dimensions of the normal brain ventricles increased gradually and steadily between the age of one and fifty years, however they increased markedly and significantly thereafter in both sexes. This may be due to a physiological brain atrophy that may be encountered in most elderly individuals. Ventricular system was larger in males than that of females of all age groups.