Several recent studies have investigated the relationship between the geographic concentration of production and vertical integration, based on the hypothesis that the spatial agglomeration of firms in the same industry facilitates input procurement, thereby reducing the degree of vertical integration. This article contributes to this debate in two ways: first, we focus on interindustry vertical integration, and second, we consider the effects on vertical integration of unrelated and vertically related variety at the local level. The latter was measured using information from input-output tables and captured the opportunities for outsourcing within the local system. A data set of 24,663 Italian business groups in 2001 was used to estimate Tobit models to investigate the influence of vertically related variety and other agglomeration forces on the degree of vertical integration of groups. We found that vertical integration is influenced by industry specialization at the local level and that higher vertically related variety reduces the need for firms to integrate activities, since they have more opportunities to acquire intermediate goods and services within the local system. We analyze the manufacturing and different macroareas and show that this relationship is also influenced by technology and differences in the organization of economic activities at the local level.