PURPOSE:To evaluate if volume or any of the three dimensions of prostate influences cancer detection rate by 12-core transrectal ultrasound (TRUS) guided prostate biopsy. MATERIALS AND METHODS:We have searched our database for patients who underwent 12 core TRUS guided prostate biopsy with PSA values between 4.0 and 9.9 ng/ml, benign digital exam and no suspicious lesions at TRUS. The measurements of three dimensions and volume of the prostate of 99 patients were correlated with cancer detection rates of biopsy. RESULTS:There were no statistically significant differences between patients with prostate cancer or with benign histopathologic result for mean age, PSA and % PSA. Patients without cancer had a significantly higher mean prostate volume (58.88 cc) than patients with cancer (48.85 cc) (P = 0.038). A volume of 48.5 cc was determined as a cut-off value above which cancer detection rate decreases. Of the three dimensions, only the difference for the craniocaudal dimension between benign and malignant groups was marginally significant (P = 0.052). CONCLUSIONS:With 12 core biopsy, cancer detection rate is lower in patients with prostates larger than 48.5 cc. Further studies comparing biopsy results with prostatectomy specimens can clarify whether these results necessitates higher number of cores for such patients.