OBJECTIVES: To demonstrate the construct validity of the Benign Prostatic Hyperplasia Impact Index (BII) in the assessment of men with Benign Prostatic Hyperplasia (BPH). METHODS: Data from two Tadalafil multi-center, double-blind, placebo-controlled Phase II clinical trials of men 45 years of age or older with moderate to severe BPH and evidence of bladder obstruction (N=281; N=1053) were included in this analysis.  Measures included BII, International Prostate Symptom Score (IPPS), IPSS Quality of Life Index (IPSS QOL), Lower Urinary Tract Symptoms Global Assessment Question (LUTS-GAQ), uroflowmetry measure peak flow rate (Qmax) and postvoid residual volume (PVR).  Data from each study were analyzed separately.  Pearson correlation coefficients were computed between the BII scores across visits and the other measures.  T-tests and general linear modeling compared BII scores of subjects with global ratings of improvement versus no improvement, and between subjects taking Tadalafil versus placebo.  RESULTS: There were strong correlations of BII with subjective measures (IPSS, IPSS QOL, LUTS-GAQ) and low correlations of BII with objective measures (Qmax, PVR) were observed in this analysis.  There were also statistically significant differences in BII at the End-of-Study Visit between subjects who improved versus subjects with no improvement (Studies 1 and 2, p<.0001) and between subjects taking Tadalafil versus subjects taking placebo (Study 1, p=0.0088; Study 2, p=0.0092).  CONCLUSIONS: Results demonstrate that BII is reliable and has construct validity. BII is well correlated with subjective measures and less correlated with objective measures, which is confirmatory of literature findings.  It is a valuable measure of the impact of BPH symptoms on health and functioning that can be useful in determining treatment options and outcomes for men with BPH.