Multiple sclerosis (MS) and its treatment have broad-ranging effects on quality of life. This article reviews recent efforts to assess the impact of MS on activities of daily living (ADLs) and health-related quality of life (HRQL), and describes the development of the Multiple Sclerosis Quality of Life Inventory (MSQLI). The MSQLI is a modular MS-specific HRQL instrument consisting of a widely-used generic measure, the Health Status Questionnaire (SF-36), supplemented by nine symptom-specific measures (covering fatigue, pain, bladder function, bowel function, emotional status, perceived cognitive function, visual function, sexual satisfaction, and social relationships). Content validation consisted of evaluating its adherence to a conceptual model of the impact of MS, and review by MS specialists (neurologists and allied health professionals), HRQL experts, patients, and caregivers. The reliability and construct validity of the MSQLI were rigorously evaluated in a field test with 300 North American patients (198 female, 102 male) with definite MS (Poser criteria) and a broad range of physical impairment (EDSS=0. 0-8.5). This article concludes by comparing the MSQLI with two other MS-specific HRQL measures (MS Quality of Life-54 (QOL-54) and Functional Assessment of Multiple Sclerosis (FAMS)) and discussing key issues to consider in selecting an HRQL instrument for a collaborative database.