Whether to make emergency contraception more easily available is an issue of longstanding policy debate.  Emergency contraception (EC) conveys no protection against sexually transmitted infections (STIs), but since it lowers the cost of unprotected sex, many worry that increased availability may increase risky sexual practices - even though economic bargaining models suggest the impact could be positive or negative.  We studied whether increased EC availability for women over age 18 was associated with a higher probability of risky sexual practices using data from the National Longitudinal Survey of Youth, 1997 from October 1999 – November 2009. We found that greater access to EC reduced the frequency of sexual activity and multiple sexual partners for women by about 12%, but also increased the probability of unprotected sex when women had multiple partners by about 22%.  This suggests policies for expanding EC access may need to be paired with education about its inability to control STI risk.