Background-Although emergency contraception (EC) is available without a prescription, women still rely on doctors' advice about its safety and effectiveness. Yet little is known about doctors' beliefs and practices in this area.Study Design-We surveyed 1800 US obstetrician-gynecologists. Criterion variables were doctors' beliefs about EC's effects on pregnancy rates, and patients' sexual practices. We also asked which women are offered EC. Predictors were demographic, clinical, and religious characteristics.Results-Response rate 66% (1154/1760). Most (89%) believe EC access lowers unintended pregnancy rates. Some believe women use other contraceptives less (27%), initiate sex at younger ages (12%), and have more sexual partners (15%). Half of physicians offer EC to all women (51%), while others offer it never (6%) or only after sexual assault (6%). Physicians critical of EC, males, and religious physicians were more likely to offer it never or only after sexual assault (odds ratios 2.1-12).Conclusion-Gender, religion, and divergent beliefs about EC's effects shape physicians' beliefs and practices.