BACKGROUND AND AIMS: HIV diagnoses have increased in Brazil from 2020 to 2023, with 54% of new diagnoses in 2023 occurring among men who have sex with men. This increase suggests a substantial need for HIV prevention, including pre-exposure prophylaxis (PrEP). We developed a fiscal health model to assess the financial impact of enhancing HIV prevention in Brazil. METHODS: The fiscal health model used a multicohort Markov structure covering 15 annual cohorts of men who have sex with men aged 15-29 years, linking individual health states (off PrEP, on PrEP, diagnosed with HIV) to 4 fiscal states that individuals could occupy across their modeled lifetime (formally employed, informally employed, unemployed, retired). The model compared the status quo (current provision of HIV prevention, i.e. daily oral PrEP) with enhanced prevention (availability of long-acting PrEP and outreach programs to increase PrEP uptake and adherence). Outcomes are presented as an average fiscal benefit-cost ratio across all age cohorts' lifetimes (discounted at 5%). Scenario analyses were conducted over the cohorts' total lifetime (including retirement phase) and preretirement lifetime using either conservative or alternative estimates (differing viral suppression and employment reduction estimates). RESULTS: In all scenarios, enhancing HIV prevention compared with status quo averts >70,000 HIV diagnoses among the modeled population of 526,046 young men who have sex with men. Enhancing HIV prevention generates a return on investment of 5% and 17% over the cohorts' total lifetimes and preretirement lifetimes, representing returns of R$0.5 billion (∼US$100 million) and R$1.7 billion (∼US$340 million), respectively. With alternative estimates, enhancing HIV prevention generates a return of 20% and 33% over the total lifetimes and preretirement lifetimes, respectively. CONCLUSIONS: Enhancing HIV prevention shows a positive return on investment. Decision-makers should consider long-term perspectives, ensuring opportunities to improve population health and contribute to a stronger economy are realized.