Human Immunodeficiency Virus (HIV)/sexually transmitted infection (STI) risk behaviors among adolescents remain significant public health concerns. Shifts in policy and advances in technology provide opportunities for researchers and clinicians to deliver and evaluate mobile-health (mHealth) prevention programs in primary care, however, research is limited. This study assessed the usability and acceptability of Storytelling 4 Empowerment—a mHealth HIV/STI and drug abuse preventive intervention app—among adolescents in primary care. Informed by principles of community-based participatory research, we recruited a purposive sample of 30 adolescents from a youth-centered community health care clinic in Southeast Michigan. The study sample is primarily African American and female. Adolescents who participated in the Storytelling 4 Empowerment intervention assessed its usability and acceptability, and self-reported their HIV/STI risk behaviors. We used a multiple-methods approach. Adolescents reported high acceptability of the content, process, and format of Storytelling 4 Empowerment, as evidenced by qualitative data and mean scores from the Session Evaluation Form for the HIV/STI and Alcohol/Drug content, overall Storytelling 4 Empowerment intervention, and Client Satisfaction Questionnaire-8. Findings indicate that Storytelling 4 Empowerment is acceptable among adolescents in primary care. A next step is to examine the effect of Storytelling 4 Empowerment on adolescent sexual risk and drug use behaviors and HIV/STI testing.