Ligamentous injuries of the ipsilateral knee have been documented in association with 25 to 35 per cent of fractures of the femoral shaft. However, to our knowledge, a similar association between ligamentous injuries of the knee and fracture of the tibial shaft has not been studied prospectively. To determine if there was such an association, a prospective study was conducted in which the knees of fifty patients who had a fracture of the ipsilateral tibial shaft of varying severity were examined manually while the patient was under general anesthesia. Eleven patients (22 per cent) were found to have sustained an injury to at least one ligament of the knee that resulted in increased laxity of 2+ or more. One knee had dislocated. On the basis of the results of this study, we believe that, after stabilization of a fracture of the tibial shaft, it is essential to examine the knee thoroughly to identify any associated ligamentous injuries.