Chronic diseases like asthma have a great impact on the everyday life of patients. Evaluation of a patient's quality of life informs us about how the patient is feeling and whether or not he or she is able to function physically, socially and emotionally. The objectives of this study were to assess the quality of life of asthmatic patients and to study the influence of age and disease severity, as independent variables, on the patient's quality of life. A 2-factor, 3-level face-centred central composite design was applied to construct a second-order polynomial model describing the effects of age and the severity on the quality of life. The second-order polynomial model was successfully applied to describe the effect of age and asthma severity with good correlation on the quality of life measured by either generic (Visual analogue scale) or disease specific (St George's Respiratory Questionnaire) instruments in the examined subjects. Our findings suggest quality of life may be used as a non-invasive patient-centred monitoring system as a guide for disease management if measured regularly.