To evaluate the effect of association of tamsulosin/tadalafil taken daily compared with tamsulosin/placebo in the lower urinary tract with urodynamic study (UDS). All patients underwent baseline UDS before randomization to tamsulosin 0.4 mg/tadalafil 5 mg (Group 1; n = 20) or tamsulosin 0.4 mg/placebo (Group 2; n = 20) once daily for 30 days. End-of-study UDS were performed on completion of the treatment period. The primary end point was to demonstrate changes in urodynamic variables in the voiding phase, detrusor pressure at maximum flow (PdetQmax), and maximum flow rate (Qmax), from baseline to week four. The primary outcome measure of this clinical trial, PdetQmax, showed a significant reduction in tamsulosin/tadalafil group (13 +/- A 17.0) compared to tamsulosin/placebo (-1.2 +/- A 14.35) group (P = 0.03). Qmax increased in both groups, tamsulosin/tadalafil (1.0 +/- A 2.4) and tamsulosin/placebo (1.4 +/- A 2.4), but the difference was not significant between treatment groups (P = 0.65). Total IPSS, storage, and voiding sub-score improved significantly in tamsulosin/tadalafil compared with tamsulosin/placebo group. The association of tamsulosin/tadalafil reduces detrusor pressure at maximum flow without changing the maximum flow rate during micturition and significantly improves lower urinary tract symptoms compared with the isolated use of tamsulosin.