PURPOSE: To investigate the relationship between changes in the posterior and anterior circulation, as seen at angiography, and the frequency and extent of cerebral infarction revealed by MR imaging in moyamoya disease. MATERIALS AND METHODS: This study involved 34 patients (22 females and 12 males, aged 2-52years) in whom cerebral angiography revealed the presence of moyamoya disease (bilateral: unilateral=24:10; total hemispheres=58) and who also underwent brain MR imaging. To evaluate the angiographic findings, we applied each angiographic staging system to the anterior and posterior circulation. Leptomeningeal collateral circulation from the cortical branches of the posterior cerebral artery (PCA) was also assigned one of four grades. At MR imaging, areas of cerebral cortical or subcortical infarction in the hemisphere were divided into six zones. White matter and basal ganglionic infarction, ventricular dilatation, cortical atrophy, and hemorrhagic lesions were also evaluated. To demonstrate the statistical significance of the relationship between the angiographic and the MR findings, both the Mantel-Haenszel chi-square test for trend and the chi-square test were used. RESULTS: The degree of steno-occlusive PCA change correlated significantly with the internal carotid artery (ICA) stage (p<0.0001). As PCA stages advanced, the degree of leptomeningeal collaterals from the PCA decreased significantly (p<0.0001), but ICA stages were not significant (p>0.05). The prevalence of infarction showed significant correlation with the degree of steno-occlusive change in both the ICA and PCA. The degree of cerebral ischemia in moyamoya patients increased proportionally with the severity of PCA stenosis rather than with that of steno-occlusive lesions of the anterior circulation. Infarctions tended to be distributed in the anterior part of the hemisphere at PCA stage I or II , while in more advanced PCA lesions, they were also found posteriorly, especially in the territories of the posterior middle cerebral artery (MCA), the posterior border zone, and the PCA (p<0.0001). The frequency of infarctions in the territories of the anterior cerebral artery (ACA) and the anterior MCA was unrelated to the degree of steno-occlusive ICA and PCA lesions (p>0.05). CONCLUSION: The degree of steno-occlusive lesions of the PCA correlated with the ICA stage. Progressive changes in steno-occlusive lesions of the ICA and PCA are associated with the extent and distribution of cerebral infarction. The degree of cerebral ischemia in moyamoya patients increased proportionally with the severity of PCA stenosis rather than with that of steno-occlusive lesions of the anterior circulation. In these patients, the presence of stenotic or occlusive PCA lesions appears to be significantly related to the occurrence of cerebral infarction.