The intention of this paper is to analyze the correlation between two techniques used to measure prostatic volume: transrectal ultrasound with planimetry and transabdominal vesicoprostatic ultrasound. A total of 44 patients have been subjected to transrectal ultrasound, where prostatic volume was determined by planimetry. With this simultaneous technique, patients were performed a vesico-prostatic ultrasound with estimation of volume, achieved by measuring the prostatic diameters and then applying the ellipsoid formula. There were no statistically significant differences between mean values of prostatic volumes as calculated by either technique, both showing a strong correlation (r = 0.817). During transrectal planimetry, the three prostatic diameters were measured and, using a multiple regression study, the influence they have on the changes of prostate's volume was noted. It was observed that it is the transverse, but essentially the longitudinal diameter, the ones which explain those changes (Sig T = 0.0012 and 0.0000, respectively).