The records of 57 patients presenting with flail chest injury from 1981 through 1987 were reviewed to determine factors affecting morbidity and mortality. Fifteen patients (26%) had 8+ rib fractures with a unilateral flail and seven (12%) had multiple rib fractures with a bilateral flail. Thirty-two (56%) had moderate-severe pulmonary contusions and 44 (77%) required chest tubes for hemo-pneumothorax. Ventilatory assistance was used in 36 (63%). The major factors determining the need for ventilatory assistance were: an ISS greater than or equal to 23, blood transfusions in the first 24 hours, moderate-severe associated injuries (fractures, head injuries or truncal organs requiring operation), and shock on admission (p less than 0.001). An adverse outcome occurred in 15 (28%); nine required ventilatory assistance greater than or equal to 14 days and six died of sepsis with pneumonia. The main factors associated with an adverse outcome were: an ISS greater than or equal to 31 (p less than 0.001), moderate-severe associated injuries (p less than 0.001), and blood transfusions (p less than 0.005). Although the primary determinants of an adverse outcome were the associated injuries and blood loss, a bilateral flail (p less than 0.01) and age greater than or equal to 50 years (p less than 0.02) were contributing factors.