A femoral shaft fracture is usually a high-energy injury and, thus, is likely to be accompanied by an injury of adjacent joints such as a knee ligament injury. However, these associated injuries are often neglected because of severe pain and deformity. The purpose of the current study is to evaluate the incidence, type and risk factors of ipsilateral knee injuries associated with femoral shaft fractures. A total of 429 femoral shaft fractures were included in this study from January 2010 to September 2015. There were 320 males and 109 females, with mean age of 40.7 years (range, 15-88). Exclusion criteria were skeletally immature patients and patients with metabolic bone disease such as osteoporosis, atypical femoral fractures, and pathologic fractures. The incidence and type of knee injury were identified, and the injury mechanisms, AO/OTA classification of the femoral shaft fractures, were analysed for assessment of risk factors for knee injuries combined with femoral shaft fractures. Knee injuries were found in 131 cases. Knee ligament injuries were identified in 87 cases. There were 20 posterior cruciate ligament injuries, 11 anterior cruciate ligament (ACL) injuries, 16 medial collateral ligament (MCL) injuries, 8 lateral collateral ligament (LCL) injuries, and 32 multi-ligament injuries. In 24 cases, ligament injuries were not detected before internal fixation of femoral shaft fractures. Average time of diagnosis for ligament injury after fixation in these neglected cases was about 10.6 weeks (range, 1-32). Fractures around the knee joint were identified in 69 cases; there were 32 patellar fractures, 14 distal femoral intra-articular fractures, 14 tibia plateau fractures, 3 proximal fibular fractures, and 6 combined fractures. Male sex, type C fracture of AO/OTA classification, and motor vehicle accidents were identified as risk factors for associated ipsilateral knee injuries in femoral shaft fractures. Knee injuries were identified in approximately 30% of femoral shaft fractures. About 30% of ligament injuries were not detected before internal fixation of femoral shaft fractures. Care should be taken since knee injuries can be accompanied by ipsilateral femoral shaft fractures.