MINNEAPOLIS—According to a recent study, low serum magnesium levels may be associated with an increased risk of ischemic stroke, partially due to its effects on hypertension and diabetes (Am. J. Epidemiol. 2009) (DOI:10.1093/aje/kwp071). Between 1987 and 1989, 14,221 men and women aged 45 to 64 years took part in the first examination of the Atherosclerosis Risk in Communities Study cohort. The incidence of stroke was ascertained from hospital records. Higher serum magnesium levels were associated with lower prevalence of hypertension and diabetes mellitus at baseline. During the 15-year follow-up, 577 ischemic strokes occurred. Serum magnesium was inversely associated with ischemic stroke incidence. The age-, sex-, and race-adjusted rate ratios of ischemic stroke for those with serum magnesium levels of 1.5, 1.6, 1.7 and 1.8 mEq/L were 1.0, 0.78, 0.70 and 0.75. After adjustment for hypertension and diabetes, the rate ratios were attenuated to nonsignificant levels. Dietary magnesium intake was marginally inversely associated with the incidence of ischemic stroke.