To improve prescribing practices for rhinopharyngitis, an interactive educational intervention and a managerial intervention were carried out in 18 primary care facilities in metropolitan Mexico City. Four family medicine clinics of the Mexican Social Security Institute (IMSS) and 14 health centres of the Ministry of Health (SSA) were included. A quasi-experimental design was employed. One hundred and nineteen physicians (IMSS 68, SSA 51) participated. Sixty-five physicians (IMSS 32, SSA 33) were in the study group, while 54 were in the control group (IMSS 36, SSA 18). The study had four stages: (I) baseline, to evaluate the physicians' prescribing behaviour for rhinopharyngitis; (II) intervention, using an interactive educational workshop and a managerial peer review committee; (III) post-intervention evaluation of short-term impact; and (IV) follow-up evaluation of long-term effect 18 months after the workshop. The control group did not receive any intervention but was evaluated at the same time as the study group. At baseline, most patients in both institutions received antibiotic prescriptions (IMSS 85.2%, SSA 68.8%). After the workshop, the percentage of patients receiving antibiotic prescriptions in the IMSS went from 85.2% to 48.1%, while in the SSA it went from 68.8% to 49.1%. Appropriateness of treatment was analyzed using the physician as the unit of analysis. At baseline, 30% of IMSS physicians in the study group treated their patients appropriately. After the intervention, this percentage increased to 57.7%, and at the 18-month follow-up it was 54.2%. The SSA study group increased the appropriate use of antibiotics from 35.7% to 46.2%, with this percentage falling to 40.9% after the 18-month follow-up period. In the control group there were no significant changes in prescribing patterns with respect to either the prescribing of antibiotics or the appropriateness of treatment. The intervention strategies were successful in both institutions. Forty per cent of physicians improved their prescribing practices after the workshop, with this change remaining in 27.5% of them throughout the follow-up period. On the other hand, 42.5% of the physicians did not change their prescribing practices after the intervention. The rest (17.5%) showed appropriate prescribing practices during all the stages of the study. We conclude that it is possible to improve the physicians' prescribing practices through interactive educational strategies and managerial interventions. This type of intervention can be an affordable way to provide continuing medical education to primary care physicians who do not have access to continuing educational activities, and to improve the quality of care they provide.