Q uality of life research contributes knowledge essential to the health and healthcare of multiple sclerosis (MS) patients. This article reviews 83 MS studies in English that have presented data on quality of life. The studies may be classified into three categories, according to the application and the main focus: 1) evaluating the development and validity of quality of life questionnaires and clinical scales (n-27); 2) evaluating factors that might influence the quality of life or comparing the quality of life among various groups (n-37); and 3) using quality of life questionnaires as outcome measures in medical trials and other interventions (n-19). The studies have shown that quality of life questionnaires more broadly measure the impact of MS than do the most frequently used measures of disease activity and effects. Using quality of life measures provides additional information in evaluating the effects of treatment and in studying the development of the disease. Such information is crucial in planning interventions for MS patients. A challenge in this field is to improve the study designs, including reaching some agreement on how to measure the quality of life.