BACKGROUND: In the past only physiological and clinical outcomes have been used to assess the effect of asthma interventions and the effect of the intervention on the lives of the patients has not been determined. The objective of this study was to assess health related impairment of quality of life in adult asthmatic patients and to develop a questionnaire for measuring quality of life in clinical trials in asthma. METHODS: Impairment of quality of life in adults with asthma was evaluated from structured interviews in which patients were asked to identify the parts of their daily lives affected by asthma. On the basis of these results, an asthma quality of life questionnaire was developed in an interviewer and self administered form and tested for comprehension and acceptability. A total of 150 adults with asthma and with a wide range of airway hyperresponsiveness were enrolled from previous clinical trials, local asthma clinics, and notices in the media. RESULTS: Areas of quality of life impairment included symptoms classically associated with asthma, responses to environmental stimuli, the need to avoid these stimuli, limitation of activities, and emotional dysfunction. Areas of impairment were similar across strata of airway hyperresponsiveness, age, and treatment requirements and between sexes, thus allowing a single questionnaire suitable for all adults with asthma to be developed. The questionnaire contains 32 items and takes 5-10 minutes to administer; in the pretesting it was shown to be acceptable to a wide range of patients. CONCLUSIONS: The questionnaire includes areas of quality of life impairment that are important to adult asthmatic patients. It has been designed to be responsive to within subject change and therefore may be used as a measure of outcome in clinical trials in asthma.