Background Sexually transmitted infections (STIs) are common among adolescents, and multiple STIs over one’s lifetime can increase health risks. Few studies have assessed lifetime STI prevalence. This study evaluates minority, underserved adolescents’ self-reported lifetime STI history and objective STI rates. Methods Lifetime STI rates of female patients at an urban adolescent health center were obtained from self-administered questionnaires. Additionally, STI test results were retrieved from electronic medical records. Results Patients reported a high lifetime prevalence of STIs. By comparing self-report and objective data, underreporting was identified for chlamydia, gonorrhea, and herpes. Conclusions STI rates in at-risk adolescent females are higher than in the general population and remain elevated over time. Lifetime STI reports could expand our understanding of sexual health and should be further studied. Underreporting, which may increase health risks and hinder health care delivery, requires further investigation. Improvements in STI screening and prevention targeting at-risk populations are warranted.