OBJECTIVE We evaluated the radiological, clinical, and functional results of femoral shaft fractures treated by interlocking intramedullary nailing. METHODS Interlocking intramedullary nailing was performed in 48 femoral shaft fractures of 46 patients (35 men, 11 women; mean age 30.5 years; range 20 to 69 years). Of the fractures, 31 were in the right femur, 13 were in the left femur, and two were bilateral. There were 44 closed and four open femoral fractures. The results were evaluated according to the Thoresen criteria. Final evaluations included 44 fractures whose follow-ups (mean 26.9 weeks; range 20 to 56 weeks) were completed. RESULTS The mean time to union was 16.5 weeks (range 12 to 42 weeks). Four patients (9%) had a varus angulation, and one patient (2.3%) a valgus angulation of 5 degrees; one patient had a posterior angulation of 10 degrees, one patient had an internal rotation of 10 degrees, and one patient had both an external rotation and valgus angulation of 10 degrees. Two patients (4.5%) developed a shortening of 2 cm. Knee flexion was 90 degrees and extension loss was 15 degrees in one patient. Knee flexion was 90 degrees in two patients, and 110 degrees in one patient. Chronic osteomyelitis developed in one patient who had a segmental femoral shaft fracture. According to the Thoresen criteria, 88.6% of patients had excellent or good results. CONCLUSIONS The high success rate obtained with interlocking intramedullary nailing makes it an appropriate method in the treatment of femoral shaft fractures in adults.