Objective: To evaluate knowledge about emergency contraception (EC) in women who are referred for treatment at the HCPA. The study investigated prevalence of use and of knowledge about correct use of the method. Study Design: Cross-sectional study. Settings: The study was conducted with patients admitted at the Hospital de Clínicas de Porto Alegre, from 2009 to 2010. Patients: Sexually active women, age range 18 to 50 years. Interventions: Patients answered a questionnaire about the use and knowledge about emergency contraception. Main Outcome Measures:  Primary outcome: prevalence of knowledge about the correct use of EC. Secondary outcome: prevalence of use of emergency contraception. Results: 61.2% of women reported using regular birth control pills, 18.7% used condoms, 9.0% used other methods, 3.0% used intrauterine device and 8.2% did not use a contraceptive method. Emergency contraception: 86.5% of interviewees reported having knowledge about the method, and 43.1% of those interviewees reported knowing how to use EC. In our study, 12.0% of interviewees correctly reported how to use EC. The prevalence of the use of EC in our sample was 19.4%. Conclusions: Though most interviewees reported having some knowledge about EC, only a small number were able to accurately describe its proper use.