This randomized clinical trial evaluated the long-term impact of an interactive seminar for physicians based on principles of self-regulation on clinician behaviour, children's use of health services for asthma, and parent's views of physician performance. Seventy-four general practice paediatricians, and 637 of their asthma patients aged 1-12 yrs, were randomized to treatment or control. Children and parents were blind to physicians' participation. Data were collected at baseline and follow-up through self-administered surveys (paediatricians), telephone interviews (parents) and medical records. The seminar focused on development of communication and teaching skills and use of therapeutic medical regimens for asthma as outlined in the National Asthma Education and Prevention Program guidelines. Approximately 2 yrs postintervention, treatment group physicians were more likely than control physicians to: use protocols for delivering asthma education (odds ratio (OR) 4.9, p=0.2), write down for patients how to adjust medicines when symptoms change (OR 5.7, p=0.05), and provide more guidelines for modifying therapy (OR 3.8, p=0.06). Parents scored treatment group physicians higher than control physicians on five specific positive communication behaviours. Children seen by treatment group physicians had fewer hospitalizations (p=0.03) and those with higher levels of emergency department (ED) use at baseline had fewer subsequent ED visits (p=0.03). No differences regarding the number of office visits were noted. There were no significant differences found between treatment and control group physicians in the amount of time spent with patients during office visits (26 versus 29 min) or in the number of patients treated with anti-inflammatory medicine. It is concluded that interactive asthma seminars for paediatricians had significant long-term benefits for their asthma care.