Background. Disruption of the normal relationship between the proximal tibia and fibula is seen in a number of different conditions such as skeletal dysplasias and post-infective deformity, as well as the consequence of lengthening procedures. Radiographic indices for the tibio-fibular relationship at the ankle have been described, but no similar measures have been reported for the proximal articulation. Aim. The purpose of this study was to investigate the normal radiographic relationship between the proximal tibia and fibula in children to determine the normal range and variation. Methods. Our radiology database was used to identify a sample of 500 normal anteroposterior radiographs of paediatric knees. All radiographs were reviewed by a single observer. The distance from the corner of the lateral tibial plateau to both the proximal tibial (PT) and fibular physes (PF) were measured, and a ratio of the two calculated (PF/PT). The process was repeated with a sample of 100 radiographs by the same observer, and a second independent observer in order to calculate intra-and inter-observer reliability. Results. The age range of patients in this study was 4–16 years, with mean age 12.7. The mean PF/PT ratio was 1.7 (standard deviation 0.2, range 1.3–2.0). Intra-observer reliability was 100% and inter-observer reliability was 97.8%. Conclusion. The results of this study demonstrate that in the normal paediatric knee, there is a consistent relationship between the position of the proximal tibial and fibular physes, with a small range of variation. The PF/PT ratio is a simple and reliable way of assessing the relationship between the proximal tibia and fibula in children, using a standard anteroposterior radiograph. This ratio could be very useful in the diagnosis and planning of surgical management of a number of different causes of tibial and fibular deformities in children