Background and Purpose— Multiple intracranial aneurysms (MIAs) are common findings of cerebral angiographies; however, MIA prevalence varies in different patient cohorts. We sought to elucidate risk factors influencing MIA prevalence and the clinical consequences. Methods— We systematically searched PubMed, Scopus, Embase, and Cochrane Library databases for publications before January 15, 2017, reporting MIA prevalence and risk factors. We used random-effects meta-analysis and multivariate regression analysis to assess the impacts of individual, study, and population characteristics. Results— We included 174 studies reporting on MIA (mean overall prevalence, 20.1%; range, 2%–44.9%) in 134 study populations with 86 989 intracranial aneurysm (IA) patients enrolled between 1950 and 2015. Studies from Europe and North America ( P <0.001) and more recent enrolment years ( P =0.046) were independently associated with higher MIA prevalence. In meta-analysis, MIA correlated with female sex (odds ratio [OR], 1.59; 95% confidence interval [CI], 1.4–1.8), higher patient age (>40 years; OR, 1.6; 95% CI, 1.14–2.25), arterial hypertension (OR, 1.51; 95% CI, 1.17–1.94), smoking (OR, 1.89; 95% CI, 1.37–2.6) and familial IA (OR, 2.02; 95% CI, 1.47–2.77), and formation of de novo (OR, 3.92; 95% CI, 1.95–7.87) and growth of initial IA (OR, 3.47; 95% CI, 1.87–6.45). Risk of subarachnoid hemorrhage in MIA patients was higher only in longitudinal studies from Japan and Korea (OR, 2.08; 95% CI, 1.46–2.96). Conclusions— Female sex, higher age, arterial hypertension, smoking, and familial IA are major risk factors for MIA. In addition, MIA patients are at risk for enhanced IA formation. Further studies are needed to evaluate rupture risk and the role of ethnicity, especially in the context of increased MIA identification with improved neurovascular imaging.