PURPOSE: To evaluate the association between knowledge about, or experience with, emergency contraception (EC), and condom use among school-attending adolescents in the state of Morelos, Mexico. METHODS: We analyzed data from anonymously self-administered questionnaires (n = 10,918), from a cluster-randomized controlled trial among first year students from 40 (75%) public high schools in Morelos, Mexico. The survey included specific questions about EC knowledge and experience as well as questions about perceived ability to negotiate and condition sexual relations on condom use; and condom use at first and last sexual intercourse. RESULTS: Overall, 61% (6384) of students had heard of EC, and 36% (1964) of girls and 39% (1997) of boys had correct knowledge about EC. Correct knowledge was based upon knowing that EC is pills taken up to 3 days after unprotected sex to prevent pregnancy. Of 1695 (15.6%) reporting lifetime sexual activity, 16.4 % (275) reported they had tried to obtain EC and almost of all them (263) reported having used EC. The probability of a student reporting he/she is capable of interrupting sexual intercourse to use a condom was significantly higher for those who had correct EC knowledge, and a history of EC use was strongly correlated with condom use at last sexual intercourse. CONCLUSIONS: Experience with emergency contraception has no adverse effects on condom use, but rather is associated with an increased probability of condom use and an increased perceived capacity to negotiate condom use. Despite concern that information about, and access to EC may encourage sexual risk taking, our results suggest the reverse is true. These data support the position that there is no justification to withhold EC information or access from adolescents.