Given increased sexual risk-taking among youth with mental health problems, this study sought to understand the developmental trajectory of sexual self-esteem (SSE) among this vulnerable population and how it is impacted by sexual experiences. Participants were 185 adolescents who attended therapeutic/alternative schools in southern New England. Changes in five domains of SSE identified by Zeanah and Schwarz (1996) were examined across adolescents who either: 1) were sexually active at baseline, 2) transitioned to activity during the study, and 3) remained inexperienced at follow-up. In support of the hypothesis that changes in SSE precede onset of experience, youth who transitioned reported higher baseline scores in the Skills domain than those who remained inexperienced. SSE was subsequently impacted by sexual activity, with differences in several domains found at baseline and follow-up across level of experience. Changes in SSE following sexual experience depended, in part, on the percentage of casual partners teens reported. (Contains 2 tables and 1 figure.)