We analyzed a consecutive series of 23 total hip arthroplasties that had been performed using modular cementless prostheses in 13 patients with a confirmed diagnosis of multiple epiphyseal dysplasia and end-stage osteoarthritis of the hip. The average Harris hip score improved from 40.6 to 93.8 points. Postoperatively, all hips demonstrated favorable alterations in the biomechanical parameters including hip center of rotation, femoral offset, femoral neck length, and limb length. At a mean follow-up of 4.8 years, no hip required revision because of aseptic loosening of the acetabular or femoral component. One patient (1 hip, 4.3%) underwent reoperation for polyethylene wear and osteolysis 8 years after index arthroplasty. This study shows encouraging clinical and radiographic outcomes of modular cementless total hip arthroplasties for this technically difficult condition.