OBJECT The authors’ aim in this paper was to determine whether periventricular anastomosis, a novel term for the abnormal collateral vessels typical of moyamoya disease, is reliably measured with MR angiography and is associated with intracranial hemorrhage. METHODS This cross-sectional study sampled consecutive patients with moyamoya disease or moyamoya syndrome at a single institution. Periventricular anastomoses were detected using MR angiography images reformatted as sliding-thin-slab maximum-intensity-projection coronal images and were scored according to 3 subtypes: lenticulostriate, thalamic, and choroidal types. The association between periventricular anastomosis and hemorrhagic presentation at onset was evaluated using multivariate analyses. RESULTS Of 136 eligible patients, 122 were analyzed. Eighteen (14.8%) patients presented with intracranial hemorrhage with neurological symptoms at onset. Intra- and interrater agreement for rating of the periventricular anastomosis score was good (κ_w = 0.65 and 0.70, respectively). The prevalence of hemorrhagic presentation increased with the periventricular anastomosis score: 2.8% for Score 0, 8.8% for Score 1, 18.9% for Score 2, and 46.7% for Score 3 (p < 0.01 for trend). Univariate analysis revealed that age (p = 0.02) and periventricular anastomosis score (p < 0.01) were factors tentatively associated with hemorrhagic presentation. The score remained statistically significant after adjustment for age (OR 3.38 [95% CI 1.84–7.00]). CONCLUSIONS The results suggest that periventricular anastomosis detected with MR angiography can be scored with good intra- and interrater reliability and is associated with hemorrhagic presentation at onset in moyamoya disease. The clinical utility of periventricular anastomosis as a predictor for hemorrhage should be validated in further prospective studies.