Relatively few studies have examined diagnostic errors in radiology. This study, conducted at a teaching hospital in Sweden, used a database of more than 19,000 radiologic studies to identify patient- and physician-specific risk factors for incorrect diagnoses. Interpretation errors occurred more frequently in children and very elderly patients (older than 85 years). Errors were also more likely when the initial interpretation was performed by a resident or by an on-call staff radiologist interpreting films outside of his or her normal specialty. An AHRQ WebM&M commentary discusses a case in which an errant initial interpretation of a CT scan led to initiation of a risky treatment plan.