Drawing on a social network perspective of organizational coordination, this paper investigates the effectiveness of coordination mechanisms on knowledge sharing in intraorganizational networks that consist of both collaborative and competitive ties among organizational units. Internal knowledge sharing within a multiunit organization requires formal hierarchical structure and informal lateral relations as coordination mechanisms. Using sociometric techniques, this paper analyzes how formal hierarchical structure and informal lateral relations influence knowledge sharing and how interunit competition moderates the association between such coordination mechanisms and knowledge sharing in a large, multiunit company. Results show that formal hierarchical structure, in the form of centralization, has a significant negative effect on knowledge sharing, and informal lateral relations, in the form of social interaction, have a significant positive effect on knowledge sharing among units that compete with each other for market share, but not among units that compete with each other for internal resources.