The aim of this study was to determine whether the polymorphism of aldosterone synthase (CYP11B2) -344C/T and angiotensin-converting enzyme (ACE) insertion/deletion (I/D) were associated with the response of blood pressure (BP) to telmisartan treatment. After a two-week single-blind placebo run-in period, 148 patients with mild-to-moderate primary hypertension received monotherapy of telmisartan with 80 mg/day and then were followed up for eight weeks. Polymorphisms of CYP11B2 -344C/T and ACE I/D gene were determined through polymerase chain reaction-restriction fragment polymorphism analysis. The relationship between these polymorphisms and changes in BP was monitored and evaluated after eight weeks of treatment. With respect to the polymorphism of CYP11B2 -344C/T, the reduction in diastolic BP was significantly greater in patients carrying the C allele (CC+CT) compared with those carrying the TT genotype. There was no significant differences between ACE I/D polymorphism and BP reduction after treatment. We concluded that the aldosterone synthase -344C/T polymorphism was related to the antihypertensive treatment with telmisartan in hypertensive patients.