This cost-effectiveness study analyzes the cost per quality-adjusted life year (QALY) gained in a randomized controlled trial that tested school support as a structural intervention to prevent HIV risk factors among Zimbabwe orphan girl adolescents. The intervention significantly reduced early marriage, increased years of schooling completed, and increased health-related quality of life. By reducing early marriage, the literature suggests the intervention reduced HIV infection. The intervention yielded an estimated US$1,472 in societal benefits and an estimated gain of 0.36 QALYs per orphan supported. It cost an estimated US$6/QALY gained, about 1 % of annual per capita income in Zimbabwe. That is well below the maximum price that the World Health Organization (WHO) Commission on Macroeconomics and Health recommends paying for health gains in low and middle income countries. About half the girls in the intervention condition were boarded when they reached high school. For non-boarders, the intervention's financial benefits exceeded its costs, yielding an estimated net cost savings of $502 per pupil. Without boarding, the intervention would yield net savings even if it were 34 % less effective in replication. Boarding was not cost-effective. It cost an additional $1,234 per girl boarded (over the 3 years of the study, discounted to present value at a 3 % discount rate) but had no effect on any of the outcome measures relative to girls in the treatment group who did not board. For girls who did not board, the average cost of approximately 3 years of school support was US$973.