OBJECTIVE: To identify the most common substantive medical errors identified by medical record review.

DESIGN: Retrospective cohort study.

SETTING: Twelve Veterans Affairs health care systems in 2 regions.

PARTICIPANTS: Stratified random sample of 621 patients receiving care over a 2-year period.

MAIN OUTCOME MEASURE: Classification of reported quality problems.

METHODS: Trained physicians reviewed the full inpatient and outpatient record and described quality problems, which were then classified as errors of omission versus commission.

RESULTS: Eighty-two percent of patients had at least 1 error reported over a 13-month period. The average number of errors reported per case was 4.7 (95% confidence intervals [CI]: 4.4, 5.0). Overall, 95.7% (95% CI: 94.9%, 96.4%) of errors were identified as being problems with under-use. Inadequate care for people with chronic illnesses was particularly common. Among errors of omission, obtaining insufficient information from histories and physicals (25.3%), inadequacies in diagnostic testing (33.9%), and patients not receiving needed medications (20.7%) were all common. Out of the 2,917 errors identified, only 27 were rated as being highly serious, and 26 (96%) of these were errors of omission.

CONCLUSIONS: While preventing iatrogenic injury resulting from medical errors is a critically important part of quality improvement, we found that the overwhelming majority of substantive medical errors identifiable from the medical record were related to people getting too little medical care, especially for those with chronic medical conditions.