Severely low and/or high body mass index (BMI) has been associated with intracerebral hemorrhage (ICH) risk in several large cohorts. The aim of this study is to assess the relationship between BMI and the presence of cerebral microbleeds. The presence and number of microbleeds were assessed on three-dimensional T2-weighted gradient-recalled-echo sequence on magnetic resonance imaging (MRI). The inclusion criteria were participants aged >40 years old without aneurysmal subarachnoid hemorrhage and any type of cerebral vascular malformations. BMI was categorized into severe underweight (<17.0 kg/m(2)), mild underweight (17.0-18.4 kg/m(2)), normal range (18.5-24.9 kg/m(2)), overweight (25.0-29.9 kg/m(2)), and obese (≥ 30.0 kg/m(2)). Multivariate analyses were adjusted for age, sex, hypertension, smoking, alcohol, stroke subtype, severity of periventricular hyperintensities and deep white matter hyperintensities, and dementia. Additionally, we conducted stratification analyses by age, ICH, smoking habit, or history of any kind of cancer, respectively. A total of 384 participants (232 males, 152 females; mean age 67.5 years) met our inclusion criteria. Overall mean BMI was 22.8 ± 3.6 kg/m(2). On multivariate analyses, severe underweight carried a significantly higher risk for cerebral microbleeds (3.48, 1.06-11.4) compared with normal range BMI, even after stratification in the subgroup aged ≥ 60 years (7.23, 1.57-33.2), nonsmokers (4.75, 1.10-20.5), noncancer subgroup (5.66, 1.31-24.5), and non-ICH subgroup (3.81, 1.14-12.7). We found that severe underweight was an independent significant risk factor for presence of cerebral microbleeds, even after effect of aging, smoking, or preexisting illness was eliminated.