Trigger tools are algorithms that prompt clinicians to investigate a potential adverse event. These tools are in routine practice for detection of adverse drug events and have been used to identify diagnostic delays. Investigators randomized physicians to either no intervention or to receive triggers related to cancer diagnosis; each trigger was an abnormal diagnostic test result for which follow-up testing is recommended. Delays in acting on abnormal test results are a known cause of adverse events. Sending reminders to physicians based on the trigger process led to higher rates of recommended diagnostic evaluation completion and a shorter time to completion for two of the three studied conditions. These promising results suggest that trigger tools could play a role in improving diagnosis across a range of conditions.