To evaluate emergency contraception (EC) knowledge and use as well as identify factors associated to correct EC knowledge among public schools students in Morelos, Mexico. Cross-sectional study conducted in 2003-2004 in a sample of 1,550 students (ages 14-24). Logistic regression was used to identify factors associated to EC correct knowledge. Among all, 40% were men and 60% women with an average age of 19 years. Sixty percent have heard about EC, nevertheless, only 45% have correct knowledge about it; 3% of sexually active students (43%) reported its use. Factors associated to EC correct knowledge are: being a woman (OR=1.66; CI 1,33, 2,06), being sexually active (OR=1.77; CI 1,43, 2,18), middle income (OR=1.87; CI 1,04, 3,37), living in a semi-urban zone (OR=1.34; CI 1,02, 1,77), drinking alcohol (OR=1.78; CI 1,42, 2,22). In Morelos, adolescents' knowledge of EC is scarce. Specific messages regarding its correct use are necessary.