This study was designed to identify a core set of items that may characterize impaired health in chronic respiratory failure (CRF) since none of the questionnaires commonly used to measure impaired health in patients with CRF were developed for use in such patients. Questionnaire items, identified from several sources, were administered to 92 patients with stable severe chronic hypoxia or hypercapnia, together with physiological measures of disease severity, the Sickness Impact Profile (SIP) and the St George's Respiratory Questionnaire (SGRQ). Of the 152 items identified, only 28 correlated with patients' perceptions of overall health and were also independent of age, sex, disease or type of treatment and did not show floor or ceiling effects. Principal components analysis identified three specific factors: "daily activities", "cognitive function", and "invalidity". The total score for the whole 28-item set correlated with other measures of disease activity, including SGRQ (r = 0.86) and SIP (r = 0.70), but not spirometry. The interquartile range of the 28-item set was wider than that of the SGRQ or the SIP. This study characterized two areas of health impairment in chronic respiratory failure that had not previously been identified: effects of impaired cognitive function on daily life, and a sense of invalidity. The measurements properties of this 28-item set suggest that it may be a more discriminative instrument for patients with chronic respiratory failure than existing questionnaires.