Background. The precise etiology of fecal incontinence (FI), which occurs frequently following external beam radiotherapy (EBRT) for prostate carcinoma is unknown. It is possibly related to pelvic nerve injury. The aim of this study was to assess the incidence of pudendal nerve dysfunction in men with FI after EBRT for prostate cancer compared to men with FI but no history of EBRT. Material and methods. Data were evaluated from 74 men with intact anal sphincters on endo-anal ultrasound (17 post-EBRT) who had been investigated for FI at a tertiary center. Wexner incontinence scores, pudendal nerve function, anorectal manometry, and rectal sensitivity were compared between the two patient groups. Results. Post-radiotherapy patients were older (77 ± 6 vs. 62 ± 17 years, p < 0.005) and had worse incontinence than those with no history of radiotherapy (Wexner score; 13 ± 3 vs. 8 ± 4; p < 0.005). Bilateral pudendal nerve terminal motor latency (PNTML) was abnormal in 87% of radiotherapy versus 22% of non-radiotherapy patients (p < 0.001) and the significant difference persisted even after correction for age differences. Anal sphincter pressures and rectal sensitivity for both groups were similar. Conclusion. There is a markedly higher incidence of pudendal nerve dysfunction in men with FI after EBRT for prostate cancer compared with men with FI from other etiologies. The increased severity of incontinence in radiotherapy patients is not matched by alterations in either anal sphincter pressures or rectal sensitivity compared to FI in non-ERBT patients.