Introduction: Transrectal ultrasound guided needle biopsy of the prostate is routinely performed to diagnose and stage prostate cancer. Also it is safe and easy procedure. Pain associated with prostate biopsy is a result of the needle passing through the prostate capsule into the stroma. Since the incidence of detected cancer seems to correlate with the number of biopsies obtained, the amount of pain is likely to increase when a greater number of core specimens are obtained at biopsy. We aimed to compare the infiltration of 1 ml (totally 2 ml) of 1 % lidocaine for each side and 3 ml (totally 6 ml) of 1% lidocaine for each side of the prostate for decreasing pain during the prostate biopsy procedure to optimize the amount of local anesthetic infiltration. Materials and Methods: Sixty patients who had undergone TRUS guided prostate biopsy were randomized into three groups. Group 1 received no anesthesia before the procedure. Group 2 received periprostatic local anesthesia bilaterally with 1 ml of 1 % lidocaine (2 ml totally) 5 minutes before the biopsy while group 3 received periprostatic local anesthesia bilaterally with 3 ml of 1 % lidocaine (6 ml totally) 5 minutes before the biopsy. To asses the pain scores, visual analog scale (VAS) was used separately for digital rectal examination, intramuscular injection of antibiotic before the biopsy; probe insertion and needle insertion during the biopsy. Results: Statistically no significant differences were found between the pain scores of the three groups for digital rectal examination, intramuscular injection and probe insertion. Mean pain scores during needle insertion in group 1 (no anesthesia), group 2 (2 ml lidocaine injection) and group 3 (6 ml lidocaine injection) were 6.28±2.55, 5.60±2.29 and 3.21±2.17 respectively. There was no significant difference between the pain scores of group 1 and group 2 (p=0.435). However, pain scores in patients receiving 3 ml of periprostatic lidocaine (6 ml totally) injection were significantly lower than the other two groups (p<0.001). Heamaturia and hematochezia after the biopsy were not significantly different in all groups. No adverse effects were observed due to intravascular absorption of lidocaine. There were no severe complications like sepsis, severe rectal bleeding or severe hematuria after the biopsies. Conclusion: Transrectal ultrasound guided needle biopsy is safe for diagnosing prostate cancer with few major but frequent minor complications. We found that, total amount of 2 ml of 1 % lidocaine is not sufficient for pain relief. We suggest a total amount of 6 ml of 1 % lidocaine should be considered for patient comfort for periprostatic nerve blockade before TRUS guided biopsy procedure. Our study indicates that ultrasound guided a total amount of 6 ml of 1% lidocaine injection of the periprostatic nerves improves patient comfort and tolerance it should be offered to men who undergo this common procedure.