Benign prostate hyperplasia (BPH) is common in elderly men. Nevertheless, the pathophysiology of low urinary tract symptoms (LUTS) may not be due only to BPH. Many men with LUTS are submitted to unnecessary medications or surgical interventions because their symptoms have not been correctly evaluated. Can diagnostic test such as serum prostate antigen (PSA), performed by nuclear medicine techniques and the trans-abdominal ultrasound determine with high sensitivity whether LUTS is due exclusively to BPH? The aim of the study was to correlate serum PSA, prostate volume (PV), intravesical prostatic protrusion (IPP), uroflowmetry measuring maximal urine flow/sec (Qmax), and the international prostate symptom score (IPSS) questionnaire, to estimate urine bladder outlet obstruction (BOO), in patients with BPH. A hundred and twelve patients with mean of age 72 +/- 8 years and LUTS were studied. All patients were examined according to the IPSS questionnaire, had their serum PSA tested and also Qmax of prostate volume and IPP by trans-abdominal ultrasound were examined. The patients were separated in groups according to serum PSA values (or= 4.1 ng/ml), prostate volume (PV< 20.20-40 and > 20 ml) and the intravesical prostatic protrusion (IPP < 5.5-10.10 mm). There was a statistical correlation between the BOO and: a) PSA (P = 0.004), b) prostate volume with P of < 0.001) and c) IPP = 0.005. On the contrary, there was no statistical correlation between BOO and IPSS, Qmax with P values 0.228 and 0.745 respectively. Receiving operating curve (ROC) showed that patients with a serum PSA value of 1.5-4 ng/ml, IPP of type II and PV 20-40 ml, had a sensitivity of 48% for PSA, of 50% for PV and of 47% for IPP and a specificity of 75%, 47% and 60% respectively. In conclusion, according to the results of this study, a more objective evaluation of BOO, which is exclusively due to BPH, should include, not only PV but also serum PSA values and IPP.