OBJECTIVES The aim of the study was to evaluate the association between physicians' understanding of the mechanism of action of the emergency contraceptive pill (ECP), their personal use of it, and their practice in informing their patients about the method and in prescribing it. METHODS The study was carried out in a sample of 3337 obstetrician-gynaecologists who responded to a mailed questionnaire. Bivariate analysis was used to test the association between physicians' personal use of the ECP, their understanding of its mechanism of action, and their practice in informing their patients about the method and in prescribing it. Multiple Poisson regression analysis was carried out to identify variables independently associated with the two dependent variables. RESULTS Multiple regression analysis showed that the percentage of physicians who had informed their patients about the ECP was significantly lower among those who had needed it themselves but had not used it and among those living in the northeast of Brazil. A significantly higher percentage of female than male physicians had provided information on the ECP. The percentage of physicians who had prescribed the ECP was significantly lower among those who had needed it themselves but had not used it and among those who believed that it caused a mini-abortion. The proportion of physicians who had ever-prescribed the ECP was greater among those who worked exclusively in private practice and among those who worked in a state capital. CONCLUSIONS The misconception that emergency contraception could cause a mini-abortion was associated with its denial to potential users, while physicians' personal experience of needing to use it favoured the likelihood of their informing potential users about it and prescribing it.