Community-Based Participatory research (CBPR) introduces new ethical challenges for HIV prevention studies in low-resource international settings. We describe a CBPR study in rural Kenya to develop and pilot a family-based HIV prevention and mental health promotion intervention. Academic partners (APs) worked with a community advisory committee (CAC) during formative research, intervention development, and a pilot trial. Ethical challenges emerged related to: negotiating power imbalances between APs and the CAC; CAC members' shifting roles as part of the CAC and wider community; and anticipated challenges in decision making about sustainability. Factors contributing to ethical dilemmas included low access to education, scarcity of financial resources, and the shortage of HIV-related services despite high prevalence.