Introduction: Racial differences in the clinical presentation, angiographic characteristics, and treatment outcomes of adult moyamoya disease (AMMD) are not well-characterized. Methods: Consecutive patients with AMMD prospectively treated at our institution from 2015-2018 were reviewed. Results: 261 patients with AMMD were enrolled (91 Asian/Pacific Islander, 128 Caucasian, 21 Hispanic, 21 Black). Asian patients were older at first clinic visit (43.6±10.8 vs. white 38.0±10.8, Hispanic 41.0±10.3, black 39.1±9.4; p=0.003). There were no differences in rates of hypertension (p=0.23) or smoking (p=0.36), but Hispanic patients had higher rates of diabetes (38% vs. Asian 16%, Caucasian 11.7%, Black 28.5%; p=0.05). All 7 patients with known familial MMD were Asian (p=0.002). There were no differences between races in terms of ischemic or hemorrhagic presentation; however, Asian patients were less likely to present with sentinel events such as headache (50.5% vs. Caucasian 71%, Hispanic 71.4%, Black 52.4%; p=0.03). On pre-operative angiography, Asians were more likely to have anterior choroidal or posterior communicating artery moyamoya collaterals (44% vs. Caucasian 30%, Hispanic 17%, Black 28.6%; p=0.004) and more extensive external carotid artery supply (4.9±10.6% vs. Caucasian 2.2±6.3%, Hispanic 1.3±4.5%, Black 1.1±3.0%; p=0.05). There were no differences in rates of peri-operative symptomatic infarct (p=0.94) or hemorrhage (p=1.0). After revascularization, moyamoya collaterals were more likely to regress/improve in Asians (59% vs. Caucasian 39.5%, Hispanic 28.6%, Black 33%; p=0.005), remain stable in Caucasians (58.6% vs. Asian 36%, Hispanic 52.4%, Black 56%; p=0.03), and increase/worsen in Hispanics (19% vs. Asian 5%, Caucasian 1.9%, Black 11%; p=0.01). At last follow-up with a mean of 1.91±1.5 years, there were no differences in functional outcomes between races (p=0.94). Conclusions: AMMD patients of Asian descent may present later in the disease course, potentially due to experiencing fewer milder symptoms such as headache that may serve as early warning signs. The effect of revascularization on regression of moyamoya collaterals may differ based on race. The clinical impact of these differences requires further investigation.