An analysis of the records of 2 130 patients who consecutively underwent median sternotomy with or without cardiopulmonary bypass showed that sternal insufficiency necessitating refixation of the sternal plates developed in 12 patients (0.56%). This complication arose during the initial hospital stay in 11 patients, but in one patient the sternal instability appeared about a year after the operation. Re-exploration showed interruption of the stainless steel wires in six cases. In the other cases the wires had loosened, or knots had opened, or wires had cut through the sternal bone. All 12 patients had undergone open-heart surgery. The commonest risk factors for sternotomy dehiscence were excessive blood loss with heavy transfusion requirements, and postoperative wound infections. Other factors were respiratory complications and postoperative ventilatory support, low cardiac output syndrome, chronic obstructive pulmonary disease and obesity. Careful closure of the sternum, using figure-of-eight sutures if necessary, and avoidance of excessive application of bone wax are important for preventing this harmful complication.