Retrospective chart review is the standard for estimating prevalence of adverse events manual review of the electronic health record (EHR) is resource intensive. This study describes the construction and validation of electronic trigger set, TriggerPrim, to rapidly identify charts with potential adverse events in primary care. The resulting set has five triggers: ≥3 appointments in a week at the PC center, hospital admission, hospital emergency department visit, prescription of major opioids, and chronic benzodiazepine treatment in patients 75 years or older. Use of TriggerPrim reduced time in the EHR by half.