When choosing a contraception method, women base their decisions on their subjective expectations about the realizations of method-related outcomes. Examples of outcomes include getting pregnant and contracting a sexually transmitted disease (STD). I combine innovative data on probabilistic expectations with observed contraceptive choices to estimate a random utility model of birth control choice. The availability of expectations data is essential to identify preferences from beliefs. Effectiveness, protection against STDs, and partner's disapproval are found to be the most important factors in the decision process. The elicited expectations and inferred preference parameters are used to simulate the impact of various policies.