The Monk Duopleet femoral interlocking uncemented two-component endoprosthesis consists of a polyethylene cup covered by a metal cap and an Austin-Moore type stem. Seventy-two patients (average age, 71 years) were treated by this arthroplasty: 27 for subcapital femoral neck fracture, 36 for osteoarthritis, and nine as an exchange operation. Three patients died following operation. After a mean follow-up time of 50 months, 47 patients were reexamined clinically and radiographically. Because of loosening, four patients had the prosthesis removed. Twenty-six patients were classified as excellent, 12 as good, six as fair, and three as poor. There were no cases of acetabular intrusion. The Monk Duopleet prosthesis may solve the problem of the loosening that had been associated with femoral component alone. The long-term results are promising and appear to be better than the results of the standard Moore prosthesis. The Monk Duopleet prosthesis is an alternative to other two-component endoprostheses for the treatment of subcapital hip fractures and in the group of patients suffering from osteoarthritis, where an arthroplasty with a cemented prosthesis may be considered hazardous because of age or general disease.