The objective of the present study was to determine the presence and level of occlusion in the cerebral arteries using three-dimensional time-of-flight (TOF) MR angiography. Routine axial T1-weighted, axial or coronal T2-weighted MR imaging, proton MR spectroscopy, diffusion-weighted MR imaging and TOF MR angiography of the brain were performed in nine patients with DDMS (five congenital and four acquired). Of congenital cases, three with an occlusion at the root of the MCA (cases 3,4,5) and one with an occlusion on M1, M2 and M3 (case 7) had severe clinical findings, and one with an occlusion on M2 and M3 (case 8) had moderate clinical findings. Cerebral encephalomalacia was found in four congenital DDMS cases (cases 3,4,7,8). Of four acquired DDMS cases; one with an occlusion on M1, M2 and M3 (case 1), and one with an occlusion on M2 and M3 (case 6) had moderate clinical findings, and one with an occlusion on M2 (case 2) and one with an occlusion on M3 (case 9) had mild clinical findings. Contrary to the congenital DDMS cases (4/5), only one of acquired cases (1/4) had encephalomalacia. Our results suggest that unilateral cerebral arterial occlusion is the main factor which results in DDMS, and the level of occlusion has a significant effect on the severity of clinical findings. TOF MR angiography, which is a non-invasive technique, provides prognostic information by showing the occluded arteries and the level of occlusion.