OBJECTIVE: To explore genetic and lifestyle risk factors of MRI-defined brain infarcts (BI) in large population-based cohorts. METHODS: We performed meta-analyses of genome-wide association studies (GWAS) and examined associations of vascular risk factors and their genetic risk scores (GRS) with MRI-defined BI and a subset of BI, namely, small subcortical BI (SSBI), in 18 population-based cohorts (n = 20,949) from 5 ethnicities (3,726 with BI, 2,021 with SSBI). Top loci were followed up in 7 population-based cohorts (n = 6,862; 1,483 with BI, 630 with SBBI), and we tested associations with related phenotypes including ischemic stroke and pathologically defined BI. RESULTS: The mean prevalence was 17.7% for BI and 10.5% for SSBI, steeply rising after age 65. Two loci showed genome-wide significant association with BI: FBN2, p = 1.77 x 10(-8); and LINC00539/ZDHHC20, p = 5.82 x 10(-9). Both have been associated with blood pressure (BP)-related phenotypes, but did not replicate in the smaller follow-up sample or show associations with related phenotypes. Age- and sex-adjusted associations with BI and SSBI were observed for BP traits (p value for BI, p [BI] = 9.38 x 10(-25); p [SSBI] = 5.23 x 10(-14) for hypertension), smoking (p [BI] = 4.4 x 10(-10); p [SSBI] = 1.2 x 10(-4)), diabetes (p [BI] = 1.7 x 10(-8); p [SSBI] = 2.8 x 10(-3)), previous cardiovascular disease (p [BI] = 1.0 x 10(-18); p [SSBI] = 2.3 x 10(-7)), stroke (p [BI] = 3.9 x 10(-69); p [SSBI] = 3.2 x 10(-24)), and MRI-defined white matter hyperintensity burden (p [BI] = 1.43 x 10(-157); p [SSBI] = 3.16 x 10(-106)), but not with body mass index or cholesterol. GRS of BP traits were associated with BI and SSBI (p