We examine the relationship characteristics associated with contraceptive method choice within young people's nonmarital sexual relationships, using data from retrospective relationship histories available in the third wave (2001-2002) of the National Longitudinal Study of Adolescent Health. Data-reduction techniques produce a detailed multidimensional characterization of relationship commitment for nonmarital sexual relationships. We then use multilevel analysis to estimate associations between two key relationship characteristics-relationship commitment and couple heterogamy-and the type of contraceptive method used at last sexual intercourse within each relationship. Results indicate that for a given individual, contraceptive method choice varies across relationships as a function of these characteristics, even after we account for important individual and family characteristics and prior relationship experiences.