PURPOSE: Medical treatment for men with lower urinary tract symptoms and prostatic enlargement secondary to benign prostatic hyperplasia is 5α-reductase inhibitor monotherapy or coadministration with an α-blocker. We assessed the effects of tadalafil 5 mg coadministered with finasteride 5 mg during 26 weeks on lower urinary tract symptoms and sexual symptoms. MATERIALS AND METHODS: In an international, randomized, double-blind, parallel study of men 45 years old or older who were 5α-reductase inhibitor naïve and had an I-PSS (International Prostate Symptom Score) of 13 or greater and prostate volume 30 ml or greater, 350 were treated with placebo/finasteride and 345 received tadalafil/finasteride for 26 weeks. Changes in lower urinary tract symptoms secondary to benign prostatic hyperplasia were assessed with the I-PSS, erectile dysfunction improvements were assessed with the IIEF-EF (International Index of Erectile Function-Erectile Function) in sexually active men and safety was assessed by evaluating adverse events. RESULTS: Least squares mean changes from baseline in I-PSS after 4, 12 and 26 weeks of tadalafil/finasteride coadministration were -4.0, -5.2 and -5.5, respectively. Corresponding values for placebo/finasteride coadministration were -2.3, -3.8 and -4.5 (p ≤ 0.022 at all visits favoring tadalafil/finasteride coadministration). I-PSS subscores (storage and voiding) and quality of life index were also numerically improved with tadalafil/finasteride coadministration. Least squares mean changes from baseline in IIEF-EF with tadalafil/finasteride coadministration were 3.7 after 4 weeks, and 4.7 after 12 and 26 weeks. Corresponding values for placebo/finasteride coadministration were -1.1, 0.6 and -0.0 (p <0.001 at all visits favoring tadalafil/finasteride coadministration). Tadalafil/finasteride coadministration was well tolerated and most adverse events were mild/moderate. CONCLUSIONS: The coadministration of tadalafil/finasteride provides early improvement in lower urinary tract symptoms in men with benign prostatic hyperplasia and prostatic enlargement. Tadalafil/finasteride coadministration also improves erectile function in men who have comorbid erectile dysfunction.