Gonarthrosis is a pathologic condition the incident of which is high in people over 50. Its etiologic factors are varus-valgus deformities, traumatic lesions, meniscal tears, osteochondritis, and metabolic diseases. The authors report their experience with the setting of a radiographic protocol for the study of 100 patients over 50. The protocol allowed both detection and quantification of: varus and valgus deformities studied in weight-bearing (teleradiography in weight-bearing) and extensor mechanism malalignment (tangential views); chondral wear of femoral and tibial joints (varus and valgus radiographs); varus and valgus knees instability (varus and valgus radiographs). The results are extremely satisfactory: this protocol allowed correct gonarthrosis grading and the evaluation of such associated lesions as lateral instability. The surgeon is thus provided with the essential elements for the choice of the correct treatment.