We assesed the efficacy ans safety of tadalafil dosed once daily for lower urinary tract symptoms secondary to benign prostatic hyperplasia. Following a 4-week, single-blind, placebo run-in 281 men were randomly assigned (1:1) to 5 mg tadalafil for 6 weeks, followed by dose escalation to 20 mg for 6 weeks or 12 weeks of placebo. Tadalafil significantly improved the mean change from baseline in International Prostate Symptom Score at 6 weeks (5 mg tadalafil -2.8 vs placebo -1.2) and at 12 weeks (5/20 mg tadalafil -3.8 vs placebo -1.7). Larger changes were observed with inclusion of the placebo run-in at 12 weeks (5/20 mg tadalafil -7.1 vs placebo -4.5). Significant improvements were also seen in the International Prostate Symptom Score irritative and obstructive domains, the International Prostate Symptom Score quality of life index, a question about urinary symptom improvement and the Benign Prostatic Hyperplasia Impact Index (significant at 12 weeks) vs placebo. International Prostate Symptom Score and International Index of Erectile Function erectile function domain scores significantly improved in the 56% of men with lower urinary tract symptoms/benign prostatic hyperplasia who were sexually active and had erectile dysfunction. Changes in uroflowmetry parameters were similar in the placebo and tadalafil groups. Commonly reported (2% or greater) treatment emergent adverse events were “erection increased,” dyspepsia, back pain, headache, nasopharyngitis and upper respiratory tract infection (each 5.1% or less). No change in post-void residual volume was seen with tadalafil treatment. Tadalafil once daily was well tolerated and demonstrated clinically meaningful and statistically significant symptomatic improvement for lower urinary tract symptoms/benign prostatic hyperplasia. Tadalafil also improved erectile function in men with lower urinary tract symptoms and erectile dysfunction.