Why are some people more altruistic than others? Morishima et al. used voxel-based morphometry to demonstrate that stronger altruistic tendencies were associated with larger grey matter volume in the right temporoparietal junction (TPJ). Furthermore, the specific conditions under which an individual makes altruistic choices were associated with TPJ grey matter volume and with increases in activation in that area. These findings demonstrate a functional and structural correlate of individual differences in altruism.