Study Objective: To examine differences in factors associated with contraceptive use between younger and older adolescent age groups, which has not previously been well described. Design: Age group-specific analyses were performed on cross-sectional survey data to identify factors associated with any contraceptive use at last sex among younger (14- to 16-year-old) and older (17- to 19-year-old) sexually active African American female adolescents; interaction analyses were used to assess whether these associations differed by age. Setting: Adolescent reproductive health clinic in Atlanta, Georgia. Participants: Sexually active African American female adolescents 14-19 years of age. Interventions: No intervention tested; cross-sectional design. Main Outcome Measure: Self-reported contraceptive use during most recent vaginal sex with a male partner. Results: The prevalence of contraceptive use at last sex was identical in both groups; however, factors associated with contraceptive use differed according to age. The only factor associated with contraceptive use in both age groups was involvement in decisions about sexual health in the most recent relationship. Associations between factors and contraceptive use significantly differed according to age. History of sexually transmitted infection, age difference with partner, discussion of condoms with partner, and concurrent partners were important factors among younger adolescents; worry about pregnancy and discussion of birth control with partner were important among older adolescents. Conclusion: Factors associated with contraceptive use at last sex differ according to adolescent age; this should be considered when designing counseling and interventions for teens, as well as research.