This paper explores three selected issues which present ethical challenges unique to the development and testing of preventive HIV vaccines. The issues are: when to move forward with large scale efficacy testing of vaccines, how to incorporate behavioral interventions into the study of vaccine efficacy, and how to plan for and mitigate social harms associated with participation in an HIV vaccine trial. Careful and ongoing consideration must be given to the ethical implications of these decisions. Proposed solutions include planning for a more complex prevention trial which would integrate the evaluation of behavioral interventions and vaccine efficacy; scrupulous attention to the process of individual informed consent and community participation; and serious and deliberate attempts to plan for, educate about, and minimize the social harms.