To clarify the intra-articular pathology of dysplastic osteoarthritis, we conducted 120 hip arthroscopies. Hips were classified radiologically into four stages: 41 prearthritic stage, 42 early-stage, 34 advanced-stage, and 3 end-stage. As the radiological stage progressed, articular cartilage degeneration became more extensive and severe. In the prearthritic and early stages, cartilage degeneration generally originated in the anterosuperior portion of the weight-bearing area of the femoral head and acetabulum. Cartilage degeneration of the acetabulum usually preceded that of the femoral head. Most detaching tears of the acetabular labrum originated in the anterosuperior area, too. In conclusion, cartilage and labrum degeneration in the dysplastic hip generally originates in the anterosuperior portion of weight-bearing area.