PURPOSE:To determine by means of MR imaging the ischemic status of parenchymal lesions in moyamoya disease. MATERIALS AND METHODS: Ninety-two MR images in 50 children with moyamoya disease were retrospectively reviewed. Ischemic parenchymal lesions were categorized according to the signal intensities of cortex and subcortical white matter. We also analyzed enhancement patterns, time sequential changes in the lesions, and the Prognosis for each patient, according to lesion type. RESULTS: Among one hundred and seventeen parenchymal abnormalities, 89 gyral lesions were seen in 43 children (86 %), predominantly in the frontal area (33.1%). Cortical parenchymal lesions were categorized as either type I - intermediate to high signal intensity (SI) on both T2 weighted (T2WI) and proton density images(PDI), and associated with low SI of the subcortical white matter; type II - high SI on T2WI and PDI, without low SI of the subcortical white matter; or type III - high SI on T2WI and iso SI on PDI. Thirty-three lesions were type I, ten were type II, and 43 were type III. Time sequential changes from type I to type II, and then to type III, were observed. The prognoses of patients with a type-I lesion were better than those of patients whose lesions were type II or III. CONCLUSION: Type I lesions presented with abnormal low signal intensity in the subcortical white matter, as seen on T2W1 images. This was the characteristic and earliest finding of ischemic parenchymal lesions in moyamoya disease; sequential MR images showed that type-I lesions progressed to type II or III.