PURPOSE: We compared the positive surgical margin rate of 2.5x and 4.3x optical loupe magnification with associated technical improvement during open radical retropubic prostatectomy. MATERIALS AND METHODS: From January 2, 2004 to September 16, 2005, 511 consecutive patients underwent open radical retropubic prostatectomy, as performed by 1 surgeon. Because 10 patients refused authorization for a retrospective chart review, 501 were evaluable. For the first 265 patients 2.5x power loupes were used and for the subsequent 236 we used 4.3x power loupes. We used the chi-square test for univariate analysis, followed by multivariate logistic regression analysis adjusted for commonly recognized predictors of positive surgical margins in the 2 successive cohorts. Focusing on the apex, which was the most commonly reported site of positive surgical margins, we include operative video segments mimicking 4.3x magnification to demonstrate the surgical precision possible at 4.3x for managing the periurethral fascial bands of Walsh and urethral transection at the prostato-urethral junction. RESULTS: Positive surgical margins were identified in 39 of 265 patients (14.7%) at 2.5x and in 12 of 236 (5.1%) at 4.3x. Apical positive surgical margins were identified in 25 of 265 patients (9.4%) at 2.5x and in 5 of 236 (2.1%) at 4.3x. On multivariate analysis 4.3x magnification was independently associated with a 75% decrease in the odds of a positive surgical margin overall and in the apex alone (p <0.001 and 0.003, respectively). CONCLUSIONS: This exploratory retrospective study suggests that, compared with 2.5x magnification, the use of 4.3x magnification with technical refinements that are not possible or deemed safe at 2.5x resulted in a substantial decrease in the positive surgical margin rate.