Analysis of eight cases of diffuse pigmented villonodular synovitis of the hip joint and a review of the literature indicate that the disease was most common in persons in their fourth and fifth decades of life. In our series of seven women and one man, the duration of symptoms ranged from two and one-half to eleven years. Typical symptoms included increasing pain in the involved hip and a limp. In all cases the disease was monarticular and there were no systemic symptoms. Roentgenographic findings were cystic changes in the acetabulum and the femoral head and neck, narrowed joint space, and occasional diffuse sclerosis of the femoral head. Needle biopsy was the most useful diagnostic procedure. Treatment included complete synovectomy in all eight patients, arthroplasty with a Vitallium cup in six, and an Austin Moore prosthesis in two. Three patients had radiotherapy. Meticulous synovectomy and grafting of the cysts combined with cup arthroplasty are recommended for treatment of this disease. Our experience with the Austin Moore prosthesis in this disease is too limited to assess its value. It is our current belief that if the femoral head is destroyed by cystic changes, an Austin Moore prosthesis should probably be used.