Using a self questionnaire we have done a domiciliary study of the perception of health and respiratory function in a population of 537 patients suffering from chronic respiratory disease. We arranged elsewhere the objective biological data of the severity of the disease represented in the computerised dossier on each patient and were able to compare this objective data to the subjective data gathered by the questionnaire. The objective data, in particular the blood gas analysis, appeared to be very weakly linked to the perception that the subjects had of their health and of their physical mobility. A study of the survival at one year showed that functional capacity and psychological approach of subjects were better predictive factors of mortality than the severity of the disease defined according to medical criteria. This study recalls the limits of standard methods of follow up for chronic respiratory failure, and stresses the importance of physical independence in these subjects: this functional indicator seems to have a value which is both descriptive as it is connected, as a whole, to the indicators of the quality of life and also prognostic as it is a better predictive factor for mortality at one year.