Background This study tests the hypothesis that a system of rapid feedback and positive reinforcement using a lottery scheme as an incentive to reduce risky sexual behaviour can be used to promote safer sexual activity and reduce HIV incidence among youth in Lesotho.

Methods An unblinded, individually randomised control trial with 3426 participants, males and females 18–30 years old drawn from 30 villages in Lesotho. The intervention linked the receipt of lottery tickets to negative results for rapid tests for curable STIs: syphilis and Trichomonas vaginalis. The study objective was to test the efficacy of the lottery incentive scheme in reducing HIV incidence. Participants were randomly assigned to either a control arm (n = 1347) or one of two intervention arms eligible to receive lottery tickets: high (n = 1116) or low (n = 963) value lottery (1,000 or 500 South African Rands). All arms received STI testing, counselling, and STI treatment every four months during two years. All participants were tested for HIV at baseline and after 16, 20 and 24 months. Village level lotteries were organised every 4 months in which STI negative individuals from the intervention arms were eligible to participate and during which 4 lottery winners (2 males, 2 females) were drawn. The primary study outcome is HIV incidence.

Results After 2 years of intervention, HIV incidence was significantly lower among study participants eligible for the lotteries (OR 0.75, 95% CI 0.58 – 0.97), especially among women (OR 0.67, 95% CI 0.52 – 0.86), and in the group eligible for the high prize lotteries (1000 Rands)(OR 0.69, 95% CI 0.50 – 0.98). No harm reported.

Conclusion The results indicate that short-term financial incentives to engage in safe sex can lead to a measurable decline in HIV incidence. It would however be advisable to replicate such an intervention in other settings.