The aim of this research was to examine the determinants of the quality of life among people with multiple sclerosis, respectively to determine the relationships between disease characteristics and the quality of life, between the dimensions of illness perception and the aspects of suffering with the quality of life, and the mediating role of the aspects of suffering in the relationship between the perception of the disease and the quality of life. 52 subjects with an average age of 47.64 years diagnosed with multiple sclerosis participated in the research. The subjects' task was to fill out a series of questionnaires, including Multiple Sclerosis Quality of Life Questionnaire, The Revised Illness Perception Questionnaire and Pictorial Representation of Illness and Self Measure Revised. The research was conducted on members of the Multiple Sclerosis Association, the Multiple Sclerosis Societies from several counties and also with personal contacts of the researcher. The duration of the disease was significantly negatively related to the physical component of the quality of life and form of multiple sclerosis showed a significant effect on the physical and mental component of the quality of life. The dimensions of illness perception showed a significant correlation with quality of life. Identity, time course, consequences, and emotional representations were negatively related to the physical component of quality of life and personal control, medical control and coherence were positively related. Consequences and emotional representations were negatively related to the mental component and personal control, medical control, coherence and perception of smoking as a cause of illness were positively related. No significant correlation was obtained between the separation of the illness from the concept of self, while the perception of the size of the illness was negatively related to both components of the quality of life. Furthermore, the perceived size of the disease fully mediates between the consequences and emotional representations as predictors and the physical component as a criterion, while it partially mediates the relationship between personal and medical control and coherence as a predictor and the physical component as a criterion. The mediation effects of the size of the disease in the relationship between the dimensions of the perception of the disease as a predictor and the medical component as a criterion were not significant. Finally, a significant effect of the perceived size of the illness on the physical and mental components of quality of life and the dimensions of consequences, coherence and emotional representation was obtained. The research hypotheses were partially confirmed, and the results contribute to the knowledge about multiple sclerosis and to the identification of quality of life factors in multiple sclerosis. Suggestions for improving future research were given, as well as suggestions for psychoeducation and improvement of standard clinical examinations, all for the purpose of increasing the quality of life of people suffering from multiple sclerosis.