Chronic non-specific lung disease (CNSLD) encompasses asthma as well as chronic obstructive pulmonary disease (COPD). Recently in health care, there has been increasing awareness in the functional, psychological and social aspects of the health of patients; their quality of life (QOL). Quality-of-life research addressing CNSLD patients has been rather underdeveloped for a long period of time. Recently, however, the importance of QOL is being increasingly recognized, and several research groups have started to study QOL in CNSLD patients in more detail. This paper describes the construction of a disease-specific QOL instrument for patients with mild to moderately severe CNSLD. Items relating to several domains of QOL were listed, and 171 CNSLD patients in general practice were asked how much of a problem each item had been (assessed on a seven-point Likert scale). After applying an item-selection procedure, a uni-dimensional QOL questionnaire was constructed consisting of 55 items divided into seven domain subscales: breathing problems, physical problems, emotions, situations triggering or enhancing breathing problems, general activities, daily and domestic activities, and social activities, relationships and sexuality. Reliability estimates of the domain subscales of the constructed questionnaire varied from 0.68 to 0.89, and was 0.92 for the QOL for Respiratory Illness Questionnaire (QOL-RIQ) total scale. A first impression of the construct validity of the questionnaire was gained by investigation of the relationship between the QOL domain subscales and several indicators of illness severity, as well as the relative contribution of illness severity variables, background characteristics and symptoms to QOL, using regression analysis. Further research to validate the questionnaire to a greater extent (construct validity, test-retest reliability and responsiveness to change) is currently taking place.