Introduction: Transrectal Ultrasonography (TRUS) guided prostate biopsy is gold standard for prostate cancer detection. This procedure is an invasive procedure that is not comfortable for most of the patients and can cause complications like rectal bleeding or infection. There is no consensus about the number and technique of the biopsy procedure for prostate cancer detection. It is clear that the usage of 16 Gauge needle provides more volume of tissue for pathological examination. Before the usage of thicker biopsy needles in our clinical applications routinely, we decided to compare the morbidities during and after and pain during the biopsy procedure between the patients in whom 18 and 16 Gauge needles used for the biopsies. Materials and methods: Fifty-eight patients who underwent prostate biopsy between May 2003 and August 2004 because of abnormal findings in digital rectal examination and/or high levels of PSA were included in the study after excluding patients with diabetes, neurological deficits, or dementia, receiving antithrombotic or anticoagulant therapy, suffering pathological events, who had undergone surgery in anal region or undergone prostatic surgical interventions previously. Patients were divided into two groups as follows: group 18G (n=30) 18 gauge needles and group 16G (n=28) 16 gauge needles were used for biopsies. Oral ciprofloxacin 500 mg (two times/day) was started day before the procedure, and was continued for 5 days. Visual analog scale (VAS) was used for detecting pain during digital rectal examination (DRE), probe insertion and biopsy procedure. Hematuria, rectal bleeding and urosepsis were investigated with daily questionnaire. Hematuria was accepted persistent when lasted more than 3 days. Ages, PSA levels, and TRUS volumes of the two groups were compared with independent t-test, and pain scores with Mann-Withney U test. Results: The mean patient ages were similar in both groups. There was no patient with urosepsis after the procedure. Three patients in group 18G and 4 patients in group 16G had persistent hematuria. Persistent rectal bleeding occurred in 1 patient in group 18G and in 1 patient in group 16G. No significant differences were seen between the two groups when pain scores of the patients were evaluated at digital rectal examination and the entrance of the probe and during the biopsy. Conclusion: Similar pain and complication rates, in patients whose underwent biopsy procedures with 16 Gauge and 18 Gauge needles is couraging for the usage of 16 gauge needles. Furthermore, better pathological examination can be expected with increased volume of obtained biopsies with similar morbidity rates. Because of our data about safety of 16 gauge needle usage for prostate biopsies we decided in our clinic for prostate cancer detection. However, prospective randomized studies in larger series are needed to determine the clinical benefit.