To enhance future STI/HIV prevention efforts, this study examined factors associated with adolescents' failure to improve their condom use behaviors after participating in an STI/HIV prevention intervention. African-American adolescent females (N = 205; M age = 17.9) in an STI/HIV prevention intervention trial completed ACASI interviews and provided self-collected vaginal swabs to assess two prevalent STIs at baseline and 6 months after intervention. Analyses compared those who increased condom use after intervention (change group) to those whose condom use did not increase (nonchange group). 43.4% did not increase their condom use after the intervention and were more likely to have an STI at followup (χ(2) = 4.64, P = .03). In a multivariate logistic regression model, the nonchange group was more likely to have (a) higher sensation seeking (AOR = .91, P = .023), (b) a boyfriend (AOR = .32, P = .046), and/or (c) a physical abuse history (AOR = .56, P = .057). There were also differences in the extent to which psychosocial mediators changed between the two groups. Findings highlight the need to tailor STI/HIV interventions to adolescents with a greater degree of sensation seeking and address key relationship characteristics and trauma histories to bolster intervention efficacy.