Structurally segregated and functionally specialized regions of the human cerebral cortex are interconnected by a dense network of cortico-cortical axonal pathways. Using diffusion spectrum imaging we noninvasively map these pathways within and across cortical hemispheres in individual human subjects. An analysis of the resulting large-scale structural brain networks reveals the existence of a structural core within posterior medial and parietal cerebral cortex, as well as several distinct temporal and frontal modules. Brain regions within the structural core share high degree, strength and betweenness centrality, and they constitute connector hubs that link all major structural modules. The structural core contains the posterior components of the human default network, and its central position within cortex suggests an important role in functional integration.