Because of the high prevalence of nonadherence, investigation for secondary hypertension is recommended only after nonadherence to medication is excluded.5 PA is one of the most common identifiable causes ofTRH. The prevalence of PA was reported to be between 1% and 10% in uncomplicated hypertension and between 7% and 20% in patients with resistant hypertension. The wide range of prevalence of PA may be related to the study design or population studied. Our study provides the first direct evidence for a difference in PA prevalence for adherent vs nonadherent patients by TDM. A high prevalence of PA was noted among adherent patients, while the prevalence of PA in nonadherent patients was similar to that reported for the general uncomplicated hypertension population.