We performed intraoperative arthrography of the knee in 12 children with congenital short femur, Blount’s disease or Ollier’s disease in whom the Ilizarov technique was used for correction of deformity, leg lengthening or both. In each case, arthrography revealed a joint surface considerably different from that assumed from plain radiographs, and resulted in a change in the placement of our reference wires before application of the frame. This gave significant improvement in the mechanical axis obtained at the time of removal of the frame. The technique is safe, cheap and easy to perform. It is a useful adjunct to the application of the Ilizarov frame when used for complex lengthening and correction of deformity in the leg