Sexual dysfunction after colorectal cancer surgery may be severe and occurs in 25% to 100% of cases. Thirty-eight patients underwent colorectal resection; eight (21%) who were totally impotent and two (5%) who had ejaculatory failure were therefore studied to better understand the neurophysiological alterations related to this type of surgery. The patients were evaluated after surgery with electrophysiological testing, including examination of the sacral reflex (SR), pudendal somatosensory evoked potential (PEP), and motor evoked potential (MEP) responses. Sudomotor skin response (SSR) was also studied in a group of patients. Of the 38 patients studied, 29 showed abnormalities: six of SR, three of PEP, six of MEP, and fourteen of SSR. Only a combination of all these tests permits correct evaluation of the sexual dysfunction.