Electronic triggers are critical tools for detecting adverse events, diagnostic errors, and other safety hazards. Researchers developed an electronic health record–based trigger tool to identify delays in abnormal mammogram follow-up at Veterans Affairs facilities. The tool was moderately effective in detecting diagnostic and treatment delays (positive predictive value 71%) and rarely failed to identify a delay (negative predictive value 93%). Inability to schedule timely follow-up and other systems issues were the most common sources of delay. This study is a rigorous example of how trigger tools can detect safety hazards and improve timely cancer diagnosis. A recent Annual Perspective describes how electronic health records can both help and hinder patient safety.