Traumatic injury to the diaphragm is a relatively uncommon injury with potential for considerable morbidity if the diagnosis is delayed or missed. This review of cases of traumatic diaphragmatic injury was undertaken in order to emphasize methods and timing of diagnosis and treatment. From 1986 through 1990, 43 cases of traumatic diaphragmatic injury were admitted to the trauma unit at Sunnybrook Health Sciences Centre, for an incidence of 2% of all new multiple trauma admissions. All patients were evaluated and treated by a dedicated trauma team. The left hemidiaphragm was injured in 32 patients, the right hemidiaphragm was injured in eight cases, and the injury was bilateral in three patients. Thirty-four patients had blunt trauma. The mean Injury Severity Score for all patients was 32. The diagnosis of diaphragmatic injury was made radiologically in 21 cases and at surgery in 22 cases. The diagnosis in all cases with penetrating trauma was made at the time of surgery. The interval between injury and definitive surgery was less than 12 hours in 39 of 43 patients. The diagnosis of diaphragmatic injury was delayed by more than 12 hours in only one patient. The other three patients were diagnosed soon after injury but their definitive surgery was delayed for other reasons. Surgical repair of the diaphragm was performed via laparotomy in 40 of 43 cases. Only one patient was repaired in a delayed fashion by thoracotomy for thoracic complications. A clear contrast can be drawn between blunt injuries and penetrating trauma.(ABSTRACT TRUNCATED AT 250 WORDS)