BACKGROUND: This study describes contraceptive understanding, sources of information and consequences of contraceptive misunderstandings among urban, young adults. STUDY DESIGN: We used qualitative data from 16 focus groups and 53 interviews with Puerto Rican and African American men and women aged 18-25 years from Philadelphia and Hartford. We categorized and compared assertions made about all contraceptive methods' side effects, effectiveness and use using an iterative process. RESULTS: Participants considered contraceptive use worthwhile but felt that it carried risks of problematic side effects and contraceptive failure, with variation among methods. Men knew most about condoms and withdrawal and trusted both more than women. Personal or second-hand experience was the dominant source of information on contraceptive understanding. Misunderstandings about contraception affected their relationships and risk of unintended pregnancy. CONCLUSION: Contraceptive understanding is a powerful determinant of contraceptive use and limits the options perceived by young adults to prevent pregnancy. Research is needed to strengthen contraceptive counseling and outreach in ways that better leverage peer influence.