Recent advances in Magnetic Resonance (MR) imaging technique have offered remarkable noninvasive diagnotic tool, MR angiography (MRA), to evaluate intracranial vascular lesion. MR angiography showed a good correlation with conventional angiography in diagnosing arteriosclerotic narrowing of intracranial arteries.In this paper, we review 3D time-of-flight MRA of the intracranial stenotic lesion and discuss potential pitfalls in flow evaluation by MRA. Because the contrast of the vessels comes from blood motion, artifactual signal loss can be caused by slight changes in normal blood streams such as eddy flow or decrease in flow velosity. Another signal loss can occur in a Maximum Intensity Projection (MIP) process. These effects lead to an apparent reduction in vessel diameter, an overestimation of stenosis and a loss of visualization of small or slow-flowing vessels. Arterial flow void on MRI, phase contrast MRA with low velosity encoding and original data before the MIP process may be useful for accurate diagnosis.