PURPOSE OF REVIEW: The WHO recommends preexposure prophylaxis (PrEP) in populations at substantial risk of HIV. Despite a number of randomized controlled trials demonstrating its efficacy, and several ongoing implementation projects, PrEP is currently only available in a few countries. Modelling studies can provide useful insights into the long-term impact of introducing PrEP in different subgroups of the population. The review summarizes studies that either evaluated the cost-effectiveness or the cost of introducing PrEP, focusing on seven published in the last year. RECENT FINDINGS: These studies used a number of different types of models and investigated the introduction of PrEP in different settings. Among men having sex with men (MSM) in North America, PrEP ranged from being cost-saving (while benefiting population health) to costing US $160,000/quality-adjusted life-year gained. Among heterosexual sero-different couples, it varied from around US $5000 to US $10,000/disability-adjusted life-year averted, when PrEP was used until 6 or 12 months after the HIV-positive partner had initiated antiretroviral therapy (ART) in, respectively, Uganda and South Africa. SUMMARY: Future cost-effectiveness studies of PrEP should consider the HIV incidence, the level of uptake, the effect of its introduction on alternative prevention approaches, and the budget impact of rolling it out.