The authors evaluated the use of conditional cash transfers as an HIV and sexually transmitted infection prevention strategy to incentivise safe sex. An unblinded, individually randomised and controlled trial of 10 villages within the Kilombero/Ulanga districts of the Ifakara Health and Demographic Surveillance System in rural south-west Tanzania. The authors enrolled 2399 participants, aged 18–30 years, including adult spouses. The primary study end point was combined prevalence of the four sexually transmitted infections, which were tested and reported to subjects every 4 months:Chlamydia trachomatis, Neisseria gonorrhoeae, Trichomonas vaginalis and Mycoplasma genitalium. The authors also tested for HIV, herpes simplex virus 2 and syphilis at baseline and month 12. Conditional cash transfers used to incentivise safer sexual practices are a potentially promising new tool in HIV and sexually transmitted infections prevention. Additional larger study would be useful to clarify the effect size, to calibrate the size of the incentive and to determine whether the intervention can be delivered cost effectively.