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Background: The evaluation of degree of ventricular enlargement should be based on established indices rather than on personal experience as this is highly subjective. Our aim was to establish normal values for Evans index in a Nigerian adult population as none has been found in the Nigerian medical literature. Materials and Methods: Axial computerized tomographic brain scans of 488 normal subjects were reviewed retrospectively. Of them, 319 (65.36%) of the patients were males and 169 (34.63%) were females; their ages ranged from 18 to 84 years with a mean age of 37.26 years. The images were acquired using a multi-slice GE Sigma excite scanner. Evans index was measured as the linear ratio of the total width of the frontal horns of the cerebral lateral ventricles to the maximum intracranial diameter. Results: The mean value for Evans index for the studied population was 0.252 ± 0.04. The EI increased with age and it was slightly higher among males. The difference in Evans value in males and females was not statistically significant. Individuals above 60 years old had the highest Evans values in both sexes. Conclusion: This study has established ranges of normal value for Evans index in a Nigerian population. It agrees with the diagnostic cut-off value of > 0.3 for hydrocephalus and it compares well with that of the Caucasians.