Abnormalities in structural connectivity might be explained in part by microstructural alterations in white matter. A number of the ENIGMA‐OCD sites (n = 19) also have diffusion tensor imaging (DTI) scans of the same participants used in the analyses of the T1‐weighted MRI measures. We compared DTI‐derived values for fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD) in 25 brain regions of OCD patients (n = 700 adults and 174 children/adolescents) and healthy controls (n = 645 adults and 144 children/adolescents) (Piras et al., 2019). We meta‐analyzed patient versus control differences across sites, adjusted for age and sex, and investigated potential associations with clinical characteristics, such as medication status, age of disease onset, duration of illness, and disease severity. Adult OCD patients showed significantly lower FA in the sagittal stratum (Cohen's d = −0.21) and posterior thalamic radiation (Cohen's d = −0.26). Lower FA in the sagittal stratum was associated with a younger age of onset (z = 2.71), longer duration of illness (z = −2.09), and a higher percentage of medicated patients in the
