One of the most challenging aspects of revision total hip arthroplasty is management of bone loss. The acetabulum is particularly difficult, with its complex morphology and proximity to major neurovascular structures. We present a reliable classification system of pelvic and acetabular bone loss based on preoperative radiographs, and this classification system directs treatment of bone loss. The type and application of allograft bone required for the reconstruction will be reviewed for each level of bone loss. Good ability to prognosticate each level of treatment is available from follow-up studies based on survival. We know of no other scientifically developed and validated classification of pelvic bone loss that predicts the likely success of the applied treatment.