BACKGROUND Vertebral artery hypoplasia (VAH) may be defined as VA flow volume below approximately 30-40 mL/min using color duplex sonography. The aim of this study was to evaluate the effect of VAH on internal carotid artery (ICA) flow volume and cerebral blood flow (CBF) volume. METHODS In this study, 17 patients with VAH and 20 control subjects with normal VA flow volume were enrolled. The patients and control subjects were 50-75 years aged. The ICA and VA flow volumes were determined by using color duplex sonography. The ICA and CBF volumes of patients with VAH were compared with control group flow volumes. RESULTS There was no statistically significant difference in flow volumes of right, left and sum of both ICA between VAH and control group. However, CBF volume was lower in patient with VAH than control group. CONCLUSIONS Evaluation of CBF using color duplex sonography is noninvasive and easily applicable to all patients and provides valuable diagnostic data. To the best of our knowledge, this is the first study demonstrating lower CBFV and normal ICA flow volume in patients with VAH.