Variability in the volume of the gray matter (GM) and white matter (WM) of the adult human brain is primarily genetically determined. In addition, total brain volume is positively correlated with general intelligence, and both share a common genetic origin. However, although genetic effects on the morphology of specific GM areas in the brain have been studied, the heritability of focal WM is unknown. Similarly, whether there is a common genetic origin of focal GM and WM structures with intelligence is unresolved. We investigated the genetic influence on the densities of focal GM and WM in brain images obtained by magnetic resonance imaging of 54 pairs of monozygotic twins and 58 pairs of dizygotic twins and 34 of their siblings. We used structural equation modeling and voxel-based morphometry for genetic analyses. To investigate the common genetic origin of focal GM and WM areas associated with intelligence, we obtained trait/inter-twin correlations in which the density of each twin's focal GM and WM areas correlates with his or her twin's psychometric intelligence quotient. Genes influenced individual differences in the left and right superior occipito-frontal bundles (heritability up to 0.79 and 0.77), corpus callosum (0.82, 0.80), visual radiations (0.69, 0.79), corticospinal tract (0.78, 0.79), medial frontal cortex (0,78, 0.83), superior frontal cortex (0.76, 0.80), superior temporal cortex (0.80, 0.77), left occipital cortex (0.85), left medial cortex (0.83), left posterior cingulate cortex (0.83), right parahippocampal cortex (0.69) and amygdala (0.80, 0.55). Intelligence shares a common genetic origin with the superior occipito-frontal, great spiracle and left WM optic radiations, and the frontal, occipital and parahippocampal GM (phenotypic correlation up to 0.35). These findings point to a neural network that shares a genetic origin with human intelligence.