BACKGROUND: Influential guidelines currently define hypertension at different thresholds of blood pressure (BP). The global May Measurement Month initiative provides a unique opportunity to estimate the potential consequences of universal lowering of BP thresholds on the prevalence of hypertension based on a large, real-world, patient-level data set. METHODS: The average of the second and third of 3 attended BP readings after 5 minutes of rest from 4 021 690 standardized, opportunistic BP screenings in various settings of the 2017 to 2019 May Measurement Month initiatives from 104 countries were analyzed to assess the demographic and phenotypic impact of 3 defined BP thresholds. RESULTS: The age- and sex-standardized median of the relative increase in rate of hypertension with a change of thresholds from ≥140/≥90 to ≥130/≥80 mm Hg was 72.3% (interquartile range, 59.3%-91.3%) among the participating countries. With a change from ≥140/≥90 to ≥120/≥70 mm Hg, the median range was 162.6% (interquartile range, 132.8%-202.6%). The increase in rate of hypertension was most pronounced in low-income (95.3% and 203.9%) and least pronounced in high-income countries (71.6% and 167.1%). CONCLUSIONS: The impact of a universal application of lower BP thresholds for the definition of hypertension would have an enormous impact on the prevalence of hypertension globally with large disparities between countries and substantial heterogeneity of demographic and phenotypic patterns, which should be confirmed in dedicated population studies. While focusing on lower BP targets may constitute an opportunity for early intervention, the potential socioeconomic consequences may pose unsurmountable obstacles for most health care systems worldwide.