Abstract Purpose: To prospectively compare the diagnostic accuracy of intravesical prostatic protrusion (IPP), detrusor wall thickness (DWT), prostate volume (PV) and serum prostate specific antigen (PSA) levels for detecting bladder outlet obstruction (BOO) and predicting acute urinary retention (AUR) secondary to benign prostatic obstruction. Patients and methods: In all, 135 men who presented with lower urinary tract symptoms due to benign prostatic enlargement were enrolled in the study; among them, 50 presented with AUR. Thirty normal men in the same age group were included and represented a control group for normative data. Their evaluation included a digital rectal examination, International Prostate Symptom Score and quality-of-life question, uroflowmetry and serum total PSA assay. Transabdominal ultrasonography was used to measure the PV, IPP DWT and post-void residual urine volume. Pressure-flow urodynamic studies were used as the reference standard test for BOO, differentiating obstructed from unobstructed bladders. DWT, IPP, PV and total PSA level served as index tests. To compare the usefulness