One hundred eight femoral shaft fractures in one hundred six adults were treated by closed intramedullary interlocked nailing. Ninety-two fractures were severely comminuted and 16 fractures were segmental. The procedures were done with the patients in the supine position. A modification of the cylinder guide for fixation of the distal screws is described. All the fractures healed in an average of 18 weeks (range, 12-24 weeks). Dynamization was performed in 15 fractures. There were two postoperative complications, which did not ultimately affect the clinical results. No infections or delayed unions were observed. Closed intramedullary interlocked nailing seems to be the treatment of choice for comminuted and segmental fractures of the femoral shaft provided that all the technical details are followed by the surgeon.