In this paper, we develop theory about the relationship between supply network complexity and the traceability of adverse events. Because adverse events in complex supply networks are frequent and sometimes catastrophic, understanding how they happen is critical for the management of quality in complex supply networks. Drawing on literatures that deal with normal accidents, traceability, transparency and network complexity, we develop propositions that help explain how traceable adverse events will be in different types of supply networks. Drawing on examples from food supply networks, we illustrate the barriers to traceability associated with different types of complex network structure. We end by discussing managerial and academic implications for the design of traceability systems and supply networks.