['We clarified the distribution of neuronal nitric oxide synthase positive nerve fibers around the prostate and factors contributing to fiber quantity.', 'We investigated 46 hemispheres of 23 nonnerve sparing radical prostatectomy specimens from patients with available preoperative International Index of Erectile Function and maximum penile circumferential change data. We performed immunohistochemical staining with neuronal nitric oxide synthase antibody, and divided the prostatic hemisphere into 6 zones to assess the distribution of neuronal nitric oxide synthase positive nerve fibers at the apex, midportion and base of the prostate. Multivariate analysis of the quantity of overall neuronal nitric oxide synthase positive nerve fibers used the variables of specimen weight, patient age, body mass index, International Index of Erectile Function and maximum penile circumferential change. A maximum penile circumferential change of 20 mm or less was considered objective erectile dysfunction.', "Median patient age was 68 years (range 57 to 74). Median International Index of Erectile Function-erectile function domain score was 12 (range 0 to 24) and median maximum penile circumferential change was 25.0 mm (range 2.70 to 38.3). Of the neuronal nitric oxide synthase positive nerve fibers 65% were distributed in a 3 to 5 o'clock sextant (p <0.001). Logistic regression analysis revealed that maximum penile circumferential change was the single significant variable (p = 0.019). The fiber count was greater in the objective erectile dysfunction group (median 1,500, range 382 to 2,760) than in the nonerectile dysfunction group (median 649, range 156 to 2,916) (p = 0.009). The fiber count was significantly different between the 2 groups in the 3 to 6 o'clock area, especially at the apex."] Does baseline erectile function alter the cavernous nerve quantity and distribution around the prostate?