Maximum tumor diameter has been shown to correlate with multiple predictors of clinical outcome in prostate cancer. In the current study, we prospectively analyze whether maximum tumor diameter is a significant predictor of prostate-specific antigen (PSA) recurrence. The study population consisted of 364 patients who underwent radical prostatectomy for prostate cancer. Prostatectomy specimens were evaluated by whole-mount processing of the entire prostate. Maximum tumor diameter was measured from the whole-mount sections of the prostate. Spearman's coefficient of rank correlation was used to correlate tumor diameter with continuous variables. T-tests or analysis of variance (ANOVA) tests were performed to determine if tumor diameter was significantly associated with other clinical and pathologic variables. The effect of clinical and pathologic variables on time to recurrence was analyzed using Cox regression. The mean tumor diameter for all patients was 1.73 cm (range, 0.02-4.40 cm). Maximum tumor diameter was associated with preoperative PSA (r=0.22, P<0.0001), prostate weight (r=-0.12, P=0.028), tumor volume (r=0.87, P<0.0001), Gleason score (r=0.29, P<0.0001), and pathologic stage (P<0.0001). Cox multiple regression was performed to test the prognostic value of maximum tumor diameter adjusting for pathologic stage, Gleason score, and surgical margin status. Increased maximum tumor diameter was associated with shorter time to PSA recurrence (hazard ratio=1.70, 95% confidence interval 1.13-2.56, P=0.01), controlling for risk factors, Gleason score, and surgical margin status. We conclude that maximum tumor diameter is a significant predictor of biochemical recurrence in patients with prostate cancer.