The cases of eighty-six patients in whom eighty-nine open fractures of the femoral shaft had been treated by intramedullary nailing with reaming were retrospectively reviewed. Twenty-seven fractures were classified as grade-I open fractures; sixteen, as grade-II open fractures; and forty-six, as grade-III open fractures. Immediate intramedullary nailing was done for fifty-six fractures, and delayed stabilization (five to seven days after delayed closure of the wound) was done for thirty-three fractures. A prerequisite for immediate intramedullary nailing was that irrigation and debridement of the open wound be done within eight hours after injury. All fractures healed in an average of 5.2 months. No infections occurred in the sixty-two grade-I, grade-II, or grade-IIIA open fractures, regardless of whether immediate or delayed intramedullary nailing was performed. Of the twenty-seven grade-IIIB fractures, infection developed in three: in one after immediate intramedullary nailing and in two after delayed intramedullary nailing. We concluded that, if a thorough and timely debridement can be accomplished, immediate intramedullary nailing of grade-I and grade-II open fractures of the femoral shaft does not increase the risk of postoperative infection. Selected patients who have a grade-III open fracture may be candidates for immediate intramedullary stabilization, depending on the degree of the patient's associated injuries and the extent of disruption and contamination of the soft tissues of the thigh.