Background: The aim of our study was to determine the normal ventricular size of the intracranial cavity based on the bicaudate index (BCI) calculation which was obtained through the computed tomography. Methods: We reviewed consecutive CT examinations in 1406 patients with symmetrical intracranial ventricular system and normal density of the white and gray matter, and without neurological deficits or psychiatric disorders. Results: Our series included 711 female and 695 male examinees; aged from 3 months to 89 years, mean age 46,3 ± 23,9 years. The positive correlation between age and bicaudate indexes was significant (p < 0.01). In our series, upper limit of the BCI (99th percentile) was 0.13 for the first three decades. In the fourth and fifth decade it increases to 0.15 and 0.19, respectively. Conclusions: After the age of 50, BCI progressively increases and rises to levels that are nearly double those found in the age group of 30 or younger. This is important in CT assessments of potential developments of hydrocephalus in older patients.