In a series of 504 patients with multiple sclerosis (MS), quality of life (QOL) and its main clinical and demographic determinants were assessed in comparison with healthy individuals. A postal questionnaire with self-completed measures of disability (Expanded Disability Status Scale, EDSS), QOL (Quality of Life Index, QLI), depressive mood (Self-rating Depression Scale, SDS), fatigue severity (Fatigue Severity Scale, FSS) and sleep quality (Pittsburgh Sleep Quality Index, PSQI) was sent to this sample of MS patients. Most patients were severely disabled; almost half were mildly to severely depressed, suffering from reduced sleep quality and/or fatigue. The multiple sclerosis patients had significantly lower QLI scores than healthy controls. EDSS and SDS scores were found to be predictors of global QLI score. Regarding the different QLI domains, mean SDS scores remained predictive for all QLI items, while mean EDSS, PSQI and FSS scores were only predictive for physical domains. Our study clearly demonstrates that depressive mood is the main factor influencing QOL. The disability status, fatigue and reduced sleep quality have an impact mainly on physical domains of life quality.