Abstract: Objective The authors previously deduced a formula for calculating the steal index (SI) for evaluation of the steal phenomena during the development of the collateral circulation resulting from unilateral carotid artery occlusion or stenosis. In this study the authors examine the application of SI in evaluating the steal phenomena of cerebral blood flow in cases of in-tracranial arteriovenous malformation (AVM). Methods The clinical data of 16 cases of AVM confirmed by both digital sub-traction angiography (DSA) and transcranial Doppler (TCD) ultrasound were analyzed retrospectively. The ratio of the mean blood velocity in the direct or indirect feeding artery (Vmfv) for the area containing AVM to the mean blood velocity in the neighboring feeding artery (Vmna), Vmfv/Vmna, was compared with SI of the corresponding arteries (SI=1-PI₁/PI₂, where PI₁ is the pulsatility index of the feeding artery and PI₂ the pulsatility index of the neighboring feeding artery), and the correlation between SI and the size of AVM was analyzed statistically. Results The Vmfv/Vmna of direct and indirect feeding arteries for AVM both exhibited positive correlation with SI (r=0.62, P<0.05, n=16; r=0.53, P<0.01, n=27), and SI appeared to be in posi-tive correlation with the size of AVM, but which failed to be supported by statistical analysis (r=0.48, P>0.05, n=12). Conclusion The sizes, types and development of the vascular bed of AVM can be evaluatea by analysis of SI derived from TCD in combination with DSA.