Abstract: In patients with benign prostatic hyperplasia (BPH), detrusor blood flow was evaluated by color Doppler ultrasonography (CDU) with the aim of revealing its possible usefulness as a measure of bladder outlet obstruction (BOO). Material and Methods: A total of 30 men with lower urinary tract symptoms (LUTS) suggestive of BPH underwent pressure flow study (PFS) and detrusor CDU. Pulsatile blood flow was measured at three sites, the anterior bladder wall and the two lateral walls, and detrusor resistive index (DRI) was calculated. The findings were compared between patients with and without BOO. Results: Between patients with and without BOO, there were significant differences for age (69.2 vs. 62.1 years P <0.005), PSA (3.9 vs. 2.6 ng/ml, P <0.05), prostate volume (45.5 vs.34.7 ml, P <0.05), bladder wall thickness (5.6 vs. 3.2 mm, P <0.001), blood flow detection (16/8 vs. 3/12, P <0.001). BOO was detected with diagnostic accuracy of 83.3% (25/30) by CDU. Conclusion: Color Doppler ultrasonography has the promise to become a possible indicator for the diagnosis of BOO. To ascertain its clinical utility in terms of BOO predictability, a prospective study in a large cohort is needed.