Background: Moyamoya disease (MMD) associated with a potentially underlying disease, such as genetic disorders or other coexisting hematological pathologies, is called quasi-MMD. This very rare disease has been characterized mainly in Asian countries, so far. As MMD reveals several significant ethnic differences, the question is raised whether characteristics of quasi-MMD would also vary among different ethnic backgrounds. Here, we report a series of 61 patients with quasi-MMD and highlight the specific clinical features of this rare disease among European Caucasians. Methods: We retrospectively identified 61 European Caucasians with quasi-MMD who were treated in our institution between 1997 and 2014. We analyzed demographic data, clinical symptoms, associated diseases, angiographic characteristics and functional hemodynamic studies. Results: Thirty-three percent of our patients were juvenile. We observed an overall female predominance of 2.8:1. Seventy-nine percent presented with a typical quasi-MMD with more pronounced unilateral and atypical quasi-MMD in pediatric population (unilateral/atypical: pediatric patients 20/15%, adults 7/7%). We identified a wide range of associated diseases. Overall, 84 and 8% of our cohort presented initially with ischemic and hemorrhagic manifestation, respectively. The hemorrhagic manifestation of quasi-MMD occurred however only in adults. Angiographic analysis revealed steno-occlusive involvement of the posterior circulation (in addition to the anterior circulation) in 31% with a higher involvement in pediatric patients (40%) compared to adults (27%). Conclusions: The characterization of our European Caucasian cohort reveals several differences when compared to reported Asian quasi-MMD cohorts and also compared to European Caucasian MMD cohort. We conclude that quasi-MMD represents a distinct disease with different ethnic clinical features.