OBJECTIVES: To determine the effect of flexible cystoscopy on the total, free, and percent-free prostate-specific antigen (PSA) values in male volunteers. Flexible cystoscopy is the standard method of evaluation of the bladder and urethra. PSA measurement is currently used in conjunction with the digital rectal examination to detect and guide management of prostate cancer. Thus, we must understand the effect of flexible cystoscopy on serum PSA levels. METHODS: Healthy men who were undergoing flexible cystoscopy and provided informed consent were enrolled in the study. The volunteers had blood taken for PSA measurement before cystoscopy and 1 and 24 hours after. The mean PSA values were compared using the paired t test. RESULTS: A total of 40 volunteers (age 22-82 years) enrolled in the study. Statistically significant increases in the total, free, and percent-free PSA values were noted at 1 and 24 hours after cystoscopy. The differences of 0.113 and 0.112 ng/mL (P < .05) in the mean total PSA level at 1 and 24 hours after cystoscopy were not clinically significant. The interassay variability was 0.053 ng/mL, with a standard deviation of 0.150 ng/mL. The standard deviation of 0150 ng/mL was greater than the 0.113- and 0.112-ng/mL differences seen in the total PSA values at 1 and 24 hours after cystoscopy. CONCLUSIONS: Statistically significant differences were noted in the total, free, and percent-free PSA levels before and after cystoscopy. Although these small differences achieved statistical significance, none were clinically significant. We have concluded that the serum PSA values are not affected by diagnostic flexible cystoscopy.