Ninety-nine open fractures of the tibial shaft were treated with unilateral external fixation with or without supplemental lag-screw fixation. We compared the results in forty-four fractures in which only external fixation was used (control group) with those in fifty-five fractures that were stabilized with lag-screws and external fixation, and we found no statistically significant differences between the two groups with respect to the time to full weight-bearing, the time to union, or the rates of delayed union, osteomyelitis, malunion, superficial or deep pin-track infection, or loosening of the pins. The limbs in which the fracture was treated with external fixation and supplemental lag-screws had more than twice the rate of refracture of the control limbs (11 compared with 5 per cent), and the percentage of fractures having supplemental lag-screw fixation that needed bone-grafting to achieve union was more than twice that in the group treated with external fixation alone. We concluded that the routine use of supplemental lag-screw fixation is not indicated in patients who have an open fracture of the tibial shaft that has been stabilized with external fixation.