Outcome assessment after hip anthroplasty is relevant both to in-depth research of specific procedures and to monitoring standards of practice. Instruments of outcome assessment should be fast, easy to use, reliable, specific to the question being asked, cost-effective, and applicable. Increasing evidence exists that patient-based outcome measures are more reliable than those based on clinicians' scores. This article reviews the types of instruments that are available and offers guidance about the outcome measures that are most approprate for orthopedic surgeons.