Social reward dependence (RD) in humans is a stable pattern of attitudes and behaviour hypothesized to represent a favourable disposition towards social relationships and attachment as a personality dimension. It has been theorized that this long-term disposition to openness is linked to the capacity to process primary reward. Using brain structure measures from magnetic resonance imaging, and a measure of RD from Cloninger's temperament and character inventory, a self-reported questionnaire, in 41 male subjects sampled from a general population birth cohort, we investigated the neuro-anatomical basis of social RD. We found that higher social RD in men was significantly associated with increased gray matter density in the orbitofrontal cortex, basal ganglia and temporal lobes, regions that have been previously shown to be involved in processing of primary rewards. These findings provide evidence for a brain structural disposition to social interaction, and that sensitivity to social reward shares a common neural basis with systems for processing primary reward information.