Objective: To compare the efficacy of self management of asthma with traditional treatment., Design: 12 month prospective randomised trial., Setting: Outpatient clinics in Finland., Subjects: 115 patients with mild to moderately severe asthma., Interventions: Patient education and adjustment of anti-inflammatory therapy guided by peak flow measurements., Main Outcome Measures: Unscheduled admissions to hospital and outpatient visits, days off work, courses of antibiotics and prednisolone, lung function, and quality of life., Results: The mean number of unscheduled visits to ambulatory care facilities (0.5 v 1.0), days off work (2.8 v 4.8), and courses of antibiotics (0.4 v 0.9) and prednisolone (0.4 v 1.0) per patient were lower and the quality of life score (16.6 v 8.4 at 12 months) higher in the self management group than in the traditionally treated group. In both groups admissions for asthma were rare., Conclusions: Self management reduces incidents caused by asthma and improves quality of life.