Background: Estimating prostate volume using less invasive transabdominal ultrasonography (TAUS) instead of transrectal ultrasonography (TRUS) is of interest in terms of identifying their agreement level. Previous reports on this subject, applied general correlation coefficient as the level of agreement. This study uses Bland-Altman method to quantify TAUS and TRUS agreement on estimating prostate volume.Methods: Total prostate gland volume of 40 patients with signs and symptoms of benign prostatic hyperplasia were measured using TAUS and TRUS. The study was carried out at the Urology Research Center, Razi Hospital, Guilan University of Medical Sciences (Rasht, Iran) from March to October 2010. Both methods were performed in one session by the same experienced radiologist. Data were analyzed using Pearson correlation coefficient and Bland-Altman method.Results: Total prostate volume estimated by TAUS and TRUS were 50.30±23 and 50.73±24.6 mL, respectively. The limits of agreement for the total prostate volume were -6.86/9.84 that was larger than predefined clinical acceptable margin of 5 mL.Conclusion: There is a lack of agreement between TAUS and TRUS for estimating the total prostate volume. It is not recommended to apply TAUS instead of TRUS for estimating prostate volume.