Diagnostic errors remain an ongoing patient safety challenge and can result in patient harm. This article describes one large pediatric hospital's experience using a systematic methodology to identify and measure diagnostic errors. The quality improvement (QI) project used five domains (autopsy reports, root cause analyses (RCAs), voluntary reporting system, morbidity & mortality conference, and abdominal pain trigger tool) and adjudication by a QI team to identify cases of diagnostic error; Morbidity & mortality conferences, RCAs and abdominal trigger tool identified the majority (91%) of diagnostic errors.