OBJECTIVES To evaluate relationship between intravesical prostatic protrusion (IPP) on transrectal ultrasonography (TRUS) and pressure-flow study (PFS) findings in patients with benign prostatic obstruction/lower urinary tract symptoms (BPO/LUTS). MATERIAL AND METHODS Between March 2006 and August 2009, we reviewed medical records of 87 patients who were underwent TRUS and PFS for evaluation of their LUTS. The patients were classified by the IPP vertical degree: less than 5 mm (group A), 5-10 mm (group B), over than 10 mm (groupC). The extent of bladder outlet obstruction was calculated as the bladder outlet obstruction index (BOOI) by the PFS. The obstruction was defined as the BOOI over 40. RESULTS Mean age was 71.1 years, and mean IPP vertical was 8.23 mm. The IPP vertical showed significant correlation with prostate volume (r=0.688, P<0.001) and transitional zone volume (TZV) (r=0.645, P<0.001), but there was no correlation between IPP and International Prostate Symptom Score, maximal flow rate, post-voided residual urine and BOOI. The IPP transverse was significantly correlated with BOOI (r=0.213, P=0.048). CONCLUSIONS The IPP vertical showed significant correlation with prostate volume and transitional volume, but not with severity of symptom, quality of life, parameters of PFS. However, the IPP transverse on TRUS was correlated with BOOI.