Abstract Background In view of the high prevalence of hypertension and the importance of adequate drug therapy in the prevention of complications, it is necessary to know the adherence to drug treatment in this population. Objective To verify adherence to antihypertensive drug treatment in Brazilian patients with hypertension using the Morisky-Green Test (MGT), relating it with demographic data. Methods Prospective, observational, multicenter, national registry study, with 2,578 hypertensive patients participating in study I, the Brazilian Cardiovascular Registry of Arterial Hypertension (I-RBH), recruited in the five regions of Brazil. The analyses carried out on the data were descriptive statistics, qui-square tests, ANOVA, and logistic regression, adopting 5% as the significance level for the tests. Results The research shows that 56.13% of patients in the sample were female; 56.71% were elderly (≥ 65 years); 55.86% were White; 52.37% were from the Southeast Region; and 59.74% were non-adherent. Logistic regression showed an independent relationship between patients’ age, ethnicity, and region with medication adherence. Conclusion Adherence to treatment is the key to reducing high rates of cardiovascular complications. The study brings a successful outcome in the relationship between the factors ethnicity, age, and region of patients with hypertension and medication adherence. To this end, it is necessary to understand these factors, considering systematic evaluation in the care of patients with hypertension and other chronic non-communicable diseases. This study is a significant contribution to multidisciplinary teams, as it highlights which risk factors interfere with medication adherence, incorporating better strategies in health education. complications population MoriskyGreen Morisky Green MGT, MGT , (MGT) Prospective observational multicenter 2578 2 578 2,57 I IRBH, IRBH RBH (I-RBH) Brazil statistics quisquare qui square tests ANOVA 5 5613 56 13 56.13 female 5671 71 56.71 ≥ ( 6 years years) 5586 55 86 55.86 White 5237 52 37 52.37 Region 5974 59 74 59.74 nonadherent. nonadherent non adherent. adherent non-adherent age ethnicity end noncommunicable communicable diseases teams education (MGT 257 57 2,5 (I-RBH 561 1 56.1 567 7 56.7 558 8 55.8 523 3 52.3 597 59.7 25 2, 56. 55. 52. 59.