The authors present an in-depth clinical, radiographic, and pathologic analysis of a 62-year-old man with massive bone reabsorption around the proximal femur in a total hip arthroplasty (THA). The THA was revised 13 years after implantation. Thirty millimeters of calcar resorption was noted radiographically. Evidence of stem bending was present on examination of the femoral implant, and marked wear of the acetabular cup was noted. The pathologic evaluation of removed calcar bone and cement revealed a histiocytic mass invading the bone. Intracellular and extracellular polymethylene debris was noted within the invasive mass. Evidence of fragmented methylmethacrylate cement was also present. The bone-cement interface in the excised calcar region contained segments that showed active bone remodelling around the cement without an interposed membrane. It is possible that this case of calcar resorption began with histiocytic activation and recruitment by polyethylene wear debris followed by active bone lysis. The process may be perpetuated by the fragmentation of cement, as motion occurred at the calcar bone-cement interface, and may represent an extreme example of a process occurring in cases of calcar resorption in general.