BACKGROUND: Repeated exposure to heat stress may adversely affect reproductive health, yet the population-level relationship between heat stress and infertility has not been well characterized. METHODS: We conducted a global ecological analysis across 174 countries and regions from 1990 to 2021. Heat exposure was quantified as the annual number of days falling into four Universal Thermal Climate Index categories: moderate, strong, very strong, and extreme heat stress. We additionally constructed a weighted score combining very strong and extreme heat stress. Associations with male and female infertility prevalence were estimated using linear mixed-effects models. RESULTS: Each additional day of very strong and extreme heat stress was associated with increases in male infertility ASPR of 1.292 (95% confidence interval [CI]: 0.675-1.908) and 1.654 (95% CI: 0.214-3.096) per 100,000 population, respectively. The corresponding increases in female infertility ASPR were 2.126 (95% CI: 0.785-3.467) and 7.133 (95% CI: 3.940-10.323) per 100,000 population, respectively. Higher weighted heat-stress scores were also consistently associated with greater infertility prevalence. CONCLUSIONS: These findings suggest that recurrent heat-stress exposure may be associated with a higher population burden of infertility and support consideration of reproductive health in climate-change adaptation and heat-protection strategies.