PurposeThis paper explores the ethics and feasibility of enrolling adolescent females in microbicide trials using data from 16-17 year old participants of the Phase 3 trial of the candidate vaginal microbicide, Carraguard. MethodsSecondary analysis was conducted to compare health, behavioral and operational outcomes between 16-17 year olds and 18-19 year olds screened for and enrolled in the trial. Analytical approaches included Kaplan-Meier survival analysis, Cox proportional hazards modeling, and generalized estimating equations (GEE) for non-survival endpoints. Resultsreveal no significant differences between the two age groups for health (STI, adverse event), risk behavior, or operational (adherence, follow up) outcomes. However, data suggest that after one year of trial participation, HIV and pregnancy incidence were higher and increased more rapidly for the 16-17 year olds than for 18-19 year olds; this finding is entirely consistent with other incidence data for HIV infection among South African youth and cannot be attributed to study participation without a comparison outside the trial. ConclusionsData from the Carraguard trial provide no evidence that inclusion of 16-17 year olds in the trial had any detrimental effect on trial participants or on the conduct of research. These data provide an argument motivating the inclusion of sexually-active adolescents aged 16-17 years old into future trials in order to avoid delaying access to an effective product for adolescents at high risk of HIV acquisition. Careful support for adolescent-inclusive protocols (including appropriate counseling) must be incorporated into study design.