We examined whether the degree of hemodynamic stress in patients with chronic occlusive cerebral vascular disease can be quantitatively evaluated with the use of perfusion-weighted magnetic resonance imaging (PWI). Thirty-six patients with moyamoya disease (mean age, 26.8 years; range, 18 to 59) underwent PWI and positron emission tomography (PET) within a month's interval. The PWI data were calculated by three different analytic methods. The cerebral blood flow (CBF) ratio, cerebral blood volume (CBV) ratio, and mean transit time (MTT) of the anterior circulation were calculated using the cerebellum as a control region and compared with PET data on the same three parameters and oxygen extraction fraction (OEF). Parametric maps of PWI attained a higher resolution than the PET maps and revealed focal perfusion failure on a gyrus-by-gyrus level. The relative CBV and MTT obtained with PWI showed significant linear correlations with the corresponding PET values (CBV, R2 = 0.47 to 0.58; MTT, R2 = 0.32 to 0.68). We also found that we could detect regions with abnormally elevated OEF and CBV based on the delay of PWI-measured MTT relative to the control region by defining a 2.0-sec delay as a threshold. The sensitivity and specificity were 92.3% and 100% in detecting regions with abnormally elevated OEF, and 20.0% and 100% in detecting regions with abnormally elevated CBV, respectively. Among the parameters obtained with PWI, our results suggested that the relative CBV value and delay of MTT might be quantitatively manipulated to assist in clinical decision-making for patients with moyamoya disease.