Abstract Background The new American Heart Association guidelines for hypertension (HT) proposed a reduction of the diagnostic cut-off point, leading to a substantial increase in the prevalence of HT. Objectives To assess the prevalence of HT determined by the traditional criteria, the AHA criteria, and home blood pressure monitoring (HBPM) in a population of young adults attending a primary healthcare unit, and its association with cardiovascular risk. Methods A cross-sectional population study on adults aged from 20 to 50 years attending a primary healthcare unit, in Rio de Janeiro, Brazil. Sociodemographic and anthropometric data, cardiovascular risk factors, office blood pressure and HBPM were registered. The diagnosis of HT was defined by traditional criteria (office BP ≥ 140 x 90 mmHg) and by the new (AHA) criteria (office BP ≥ 130 x 80 mmHg). Bivariate analysis was used for comparisons between the two diagnostic criteria, and Kappa coefficient was used to assess the agreement in diagnosis between office BP and HBPM. The level of significance adopted was 5% (p<0.05). Results A total of 472 individuals were evaluated (male: 39%; mean age: 38.5 ± 8.7 years). The prevalence of HT was 23.5% and raised to 41.1% with the new AHA criteria. The prevalence of HT using HBPM was 25.5%, but the diagnostic agreement was low (kappa=0.028) with changes in diagnosis in 18% of the cases. Conclusion The prevalence of HT almost doubled with the new AHA diagnostic criteria for HT. HBPM seemed to be an important instrument in HT diagnosis in this population. (Int J Cardiovasc Sci. 2021; [online].ahead print, PP.0-0)