AIMS - A number of physical and psychological factors have been shown to affect health-related quality of life (HRQoL) in patients with multiple sclerosis (MS). Among these, the role of illness perceptions has not been established as an independent factor. This study, the first of its kind in an Australian population, aimed to use a large sample to determine the relative importance of individual factors to each domain of HRQoL, in particular the role of illness perception. MATERIALS AND METHODS - 580 patients with confirmed MS were assessed cross sectionally in a designated research clinic to determine the relative impact of physical factors (illness severity, duration, age, fatigue and pain) and psychological factors (mood, cognition and illness representations) on each domain of the SF-36. RESULTS - Categorical regression analysis showed that a combination of physical and psychological factors predicted 38-71% of variance in HRQoL. Illness perception was shown to have an independent effect on HRQoL in MS. The Extended Disability Status Scale was a significant determinant in all domains except for mental health. Depression was less prevalent than anxiety, but had a greater effect on function. CONCLUSION - Illness perception is an independent factor contributing to HRQoL in people with MS. Individual domains of HRQoL are associated with different patterns of physical and psychological factors. In the domains of role and social function, activities most highly valued by patients with MS, depression, anxiety, fatigue and illness perceptions are key determinants, all of which have the potential to be improved through specific interventions.