Purpose: We determined the efficacy and safety of a relatively high dose of terazosin (5 mg) in Korean patients with lower urinary tract symptoms (LUTS), with or without concomitant hypertension. Materials and Methods: From July to December 2006, 200 men who consecutively presented with LUTS were prospectively studied. Eight weeks after treatment, blood pressure (BP), uroflowmetry, and International Prostate Symptom Score (I-PSS) were assessed. For analysis purposes, patients were stratified according to concomitant hypertension. Of the 200 patients, 173 completed the scheduled eight-week treatment period. Results: At baseline, no differences were evident in the two groups in terms of I-PSS, Qmax, PVR and BP. After eight weeks of treatment-although I-PSS and uroflowmetry parameters were not significantly different in the two groups-systolic and diastolic BP in the non-hypertensive control group were higher than in the hypertensive group (p= 0.001 and p = 0.0100, respectively). Changes in I-PSS, uroflowmetry parameters, and BPs measured at week eight post-treatment commencement did not significantly differ between the two groups. Moreover, the addition of 5 mg of terazosmi to antihypertensives did not cause a significant reduction in either systolic or diastolic BP in either group. Conclusion: Adding terazosin to existing antihypertensive regimens did not seem to increase the incidence of adverse events. Our findings suggest that 5 mg terazosin is effective and that it has an acceptable safety profile as an add-on therapy for patients with LUTS and concomitant hypertension.