Two patients, mother and daughter, had major hip joint problems related to osteopetrosis consisting of (1) subtrochanteric femoral fractures including delayed union, septic nonunion, and failed intramedullary fixation; and (2) coxa vara with symptomatic osteoarthrosis. Total hip arthroplasty (THA) was performed on three hips of these two patients, and the patients were followed for more than three years. One patient continues to ambulate without pain or the need for external support, and the potential for ambulation was established for the second patient, compromised only by her poor motivation. The greatest challenge in all these surgical procedures was the creation of an intramedullary canal in osteopetrotic bone without a semblance of an intramedullary canal. The bone ends presented a solid white amorphous appearance, indistinguishable from the cortex. Great care was required to avoid shattering this brittle bone, also during drilling and reaming. Preoperative assessment of the medullary canals is mandatory. Variations in the intramedullary canals present great difficulties in osteotomizing, reaming, and drilling osteopetrotic bone. However, subtrochanteric femoral fracture can be treated by cemented THA in patients with osteopetrosis.