OBJECTIVE To investigate the predictive value (PV) for all prostate cancers and for clinically significant cancer undiagnosed after a 10-core biopsy protocol, as the 10-core transrectal ultrasonography-guided biopsy is considered the standard technique of prostatic biopsy due to its high rate of detection of prostatic adenocarcinoma. PATIENTS AND METHODS In all, 132 consecutive radical prostatectomy (RP) specimens, with their corresponding 10-core biopsies, were reviewed. Cases with unilateral core involvement by prostate cancer were retained for study. Morphometric analysis was conducted on the biopsy-negative hemi-prostates to determine the PV of the biopsy protocol with respect to the size, position and clinical significance of the lesion. RESULTS In all, 70 resected prostates (RP) had unilateral core involvement by prostate cancer. In 38 cases, there was cancer in the biopsy-negative hemi-prostates (group 1); in the remaining 32 the hemi-prostates were free of cancer (group 2). Group 1 was categorized by morphometric criteria. Specifically, 23 cases had one to eight foci of prostate cancer in the posterior nontransitional zone (NTZ) (group 1a), while 15 had two to six foci of prostate cancer in the transitional zone (TZ), or the anterior horn (AH) of the peripheral zone or the TZ and AH (group 1b). There were two cases with clinically significant prostate cancer in group 1a, and six in group 1b. CONCLUSIONS The PV of a negative five-core biopsy protocol on a hemi-prostate is 54% for prostate cancer and 11% for clinically significant prostate cancer. Most clinically significant prostate cancers were in the AH/TZ of the prostate. [ABSTRACT FROM AUTHOR]