As adolescents turn to online resources for health information, obstetricians and gynaecologists can play an active role in creating evidence-based resources for sexual health education. The purpose of this study was to assess the effect of a sexual health education website on adolescent girls' reproductive health knowledge and self-efficacy. It took the form of a prospective study among girls aged 14-18 in a rural area of the USA. Informed consent and parental consent were obtained. Participants completed a pre-test survey containing a 20 question validated Reproductive Health Knowledge Index (RHKI) and six self-efficacy questions. They then completed the website curriculum (www.marshallteentalk.org), followed by a post-test survey containing RHKI and same self-efficacy questions. Thirty-three girls completed the study with an average age of 16.42 (SD 1.09). Ten (30.3%) reported never having received sexual health education in school. Overall mean RHKI score improved from pre-test to post-test (87.67 SD 6.35 vs 90.82 SD 7.45, p = 0.012). Change in knowledge score ranged from -16.25 to+19.17 with a mean increase of+3.14 (SD 6.77). A greater proportion of participants reported improved confidence in obtaining birth control, recognising an unhealthy relationship, and getting tested for STIs.