In the international Drug Education Project, a new educational program for peer groups of doctors was developed and tested to improve the treatment of asthma patients in The Netherlands, Norway, Sweden, and Slovakia. Individualized feedback on prescribing and the underlying decision strategy was presented and discussed within the group of doctors, in relation to existing guidelines. In a parallel, randomized controlled design the effect on competence and actual prescribing was tested. Results were related to national guidelines. In general, the program improved the doctors' attitudes as well as some of their prescribing behavior. The proportion of patients treated with inhaled corticosteroids significantly improved in The Netherlands (effect size 1.27), and the proportion of oral corticosteroid use for exacerbation treatment increased both in The Netherlands and in Norway (effect sizes 1.99 and 0.87, respectively). Overall attitudes of Dutch and Norwegian doctors also improved significantly (effect sizes 1.06 and 0.87, respectively), as did both knowledge (effect size 1.06) and attitudes (effect size 1.49) concerning exacerbation treatment in Slovakia. In Sweden no significant improvements could be measured. Conclusively, improvements in asthma treatment are possible with an educational program based on self-learning in small peer groups, although effects in one health care setting may not occur in another health care setting. Possible explaining factors may be different attitudes to and experiences with guidelines as well as with continuing medical education programs, and differences in the opportunities for change, including prevailing trends in prescribing behavior.