We examined whether the time-averaged maximum velocity (TAMV), flow volume (FV) or cross-sectional area (CA) in the vertebral arteries (VA) as determined by ultrasonography was related to vascular lesions or variations in the intracranial part of the posterior circulation. Three hundred nine patients without severe stenosis in the carotid circulation (159 males, 150 females, mean age of 69.1 years) underwent both colour duplex ultrasonography and magnetic resonance angiography (MRA) and were thus analyzed. According to the MRA findings, the patients were divided as follows; 22 patients with severe stenosis in the bilateral PCA or VA or basilar artery (V group) and 287 patients without (N group). The N group was then further divided as follows; 144 patients with no (P0 group); 89 with one (P1) and 54 with both posterior communicating arteries (P2) detected on MRA. TAMV, FV and CA were compared among these groups. Both TAMV and FV of V group were significantly lower than those of N group (35.3 vs. 42.6 cm/sec in TAMV, 98.2 vs. 135.3 mL/min in FV, p < 0.001 and 0.0001, respectively). The FVs and CAs in the P0 through P2 groups were all significantly different according to the number of posterior communicating arteries (149.3 vs. 128.0 vs. 109.8 mL/min, 22.5 vs. 20.2 vs. 16.5 mm2, both p < 0.001) while TAMVs in these groups did not differ substantially. The FV in both VAs were thus found to be related to the vascular lesions or variations in the posterior circulation.