Femoro-acetabular impingement is an etiology of early osteoarthritis. It is a dynamic theory of development of arthritis due to bony deformations of the acetabulum or the proximal femur. The impingement is diagnosed clinically by the impingement and apprehension tests. The realisation of reproducible and technically irreproachable standard X-Rays is of first importance to detect the subtle but present signs of impingement. The MR arthrography is the best exam for detection of intra-articular pathologies with radial sequences allowing to establish a precise topography of the lesions. The treatment is most of the time surgical to avoid progression of cartilage lesions, either by an open surgical dislocation or arthroscopically for selected cases.