Overweight or obese body habitus is associated with cognitive deficits, impaired brain function, gray matter atrophy, and white matter (WM) hyperintensities. However, few diffusion tensor imaging (DTI) studies have assessed WM integrity in relation to overweight or obese status. This study assessed relationships between body mass index (BMI) and values of DTI parameters among 51 normal weight (lean), overweight, and obese participants who were otherwise healthy. BMI correlated negatively with fractional anisotropy and axial eigenvalues (λ1) in the body of corpus callosum (CC), positively with mean diffusivity and radial eigenvalues (λ⟂) in the fornix and splenium of CC, and positively with λ1 in the right corona radiata (CR) and superior longitudinal fasciculus (SLF). These data indicate that BMI correlates negatively with WM integrity in the fornix and CC. Furthermore, the different patterns of BMI-related differences in DTI parameters at the fornix, body, and splenium of the CC, and the right CR and SLF suggest that different biological processes may underlie BMI-related impairments of WM integrity in different brain regions. Hum Brain Mapp, 2013. © 2011 Wiley Periodicals, Inc.