This study analyzed the relationship between four renin-angiotensin system (RAS) gene polymorphisms and the response to blood pressure lowering and development of microalbuminuria in 206 patients with essential hypertension treated once daily for 12 months with telmisartan 80 mg. Seated cuff blood pressure and urinary albumin excretion (UAE) were measured throughout the study. Patients were screened for the presence of the A-6G variant of the angiotensinogen gene, angiotensin-converting enzyme insertion/deletion polymorphism, and the A1166C and C573T polymorphisms of the angiotensin II type 1 receptor gene. No significant association was found between the presence of any gene polymorphism and the reduction of blood or UAE following telmisartan treatment. The results indicate that these RAS gene polymorphisms do not affect the antihypertensive activity and renoprotection in mild-to-moderate hypertensive patients treated with telmisartan.