The aim of this study was to compare the health-related quality of life (HRQL) of asthma patients treated according to the 1997 National Institute of Health (NIH) international asthma guideline and that of asthmatics receiving non-guideline treatment. The suitability of 146 asthmatics' medication regimes was determined according to the 1997 NIH asthma guideline. Quality of life was assessed on a seven-point scale using the Asthma Quality of Life questionnaire. Just over half of the patients were not currently using the treatment considered necessary for controlling their asthma. Patients treated according to the guideline (n=72) had a significantly higher overall HRQL than patients with non-guideline treatment (5.7 versus 5.3). The differences were also significant for the subscales measuring symptoms and environmental exposure, but not for activities or emotional function. An association between non-guideline treatment and a poorer health-related quality of life in asthma patients treated in general practice was observed. This study supports the role of evidence-based guidelines in daily practice. Further studies are needed to determine if guideline treatment is responsible for the increase in health-related quality of life observed in this work.