Missed injuries have a bad reputation and are sometimes associated with serious morbidity for the patient and personal embarrassment for the surgeon. During a 10-year period, 123 missed injuries in 117 patients requiring re-operation were encountered in one trauma center. A retrospective review of causes and patterns was undertaken. The most common presentation was delayed hemorrhage (64 injuries). The colon, thoracic vasculature, chest wall arteries, and diaphragm were the most frequently involved sites. Forty-six injuries were overlooked during the diagnostic work-up, and 43 were missed during surgery. Technical problems with diagnosis and surgery accounted for 62% of missed injuries, whereas decision and judgment errors accounted for the rest. Further insight was provided by the classification of missed injuries into three types. Type I (20%) occurred outside the body area of clinical focus, whereas type II (69%) occurred within it. Type III (11%) resulted when instability of the patient necessitated interruption of the diagnostic work-up or exploration. Each type represents a different clinical pattern and dictates a specific preventive strategy.