Assessment of health-related quality of life (HRQOL) using patientreported outcomes in arthroplasty has become popular because it provides a unique perspective on successful elective procedures. However, challenges exist in the assessment of HRQOL in clinical practice and in clinical research. Patient compliance with multiple and sometimes lengthy HRQOL assessments administered at multiple follow-up visits is problematic. Many well-validated HRQOL instruments are available, and progress has been made in defining the minimal clinically important difference in hip and knee arthroplasty that denotes the minimal change perceived to be important by patients. Challenges in understanding the literature are attributable to the use of various HRQOL scales, with different scoring ranges and scoring algorithms, different interpretations of highest score, and differences in the presentation of raw versus transformed scores. Copyright 2010 by the American Academy of Orthopaedic Surgeons.