(248/450)Background: Adverse drug events (ADEs) are unintended and harmful events related to medications. ADE outcomes are important for patients, quality improvement, drug safety research, and post-marketing surveillance; yet they are vastly underreported. Objective: Our objectives were to identify barriers to ADE documentation and factors contributing to underreporting. Methods: This qualitative study was conducted in one ambulatory centre and three hospitals in British Columbia between March 2014 and December 2016. We completed workplace observations and focus groups with family, hospitalist and emergency physicians, and hospital and community pharmacists. We analyzed field notes by coding and iteratively analyzing our data to identify emerging concepts, generate thematic and event summaries, and create workflow diagrams. Clinicians validated emerging concepts by applying them to cases from their clinical practice. Results: We completed 238 hours of observations during which clinicians investigated 65 suspect ADEs. The observed events were often complex and diagnosed over time, requiring the input of multiple providers. Providers documented ADEs in charts to support continuity-of-care, but never reported them to external agencies. Providers faced time constraints, and reporting would have required duplication of documentation. Conclusions: Existing reporting systems are not suited to capture the complex nature of ADEs nor adapted to workflow, and simply not used by frontline clinicians. Systems that are integrated into electronic medical records (EMRs), make use of existing data to avoid duplication of documentation, and generate alerts to improve safety may address the shortcomings of existing systems, and generate robust ADE data as a byproduct of safer care.