Post-operative urinary retention (POUR) is a frequent complication reported as ranging from 10 to 55% in the literature. In a recent retrospective study from Laliberte et al in Quebec City, we observed that 19% of the patients operated using transanal endoscopic microsurgery (TEM) had a post-operative urinary retention (POUR). Factors related to the patient, the tumor and the surgery were not observed to be associated risk factors. Tamsulosin has been shown as an effective preventive agent of POUR for certain ano-rectal and inguinal surgeries. The efficacy of this prophylactic therapy in transanal endoscopic microsurgery has not been studied yet and is unclear considering the particularities of this procedure. TEM uses a rigid proctoscope of four centimeters of diameter and creates a continuous pneumorectum (insufflation of the rectum during all the procedure). We think that these two elements, which cause local inflammation, may be part of the reason explaining the high incidence of post-operative urinary retention after TEM procedures. The objective of our multicenter clinical trial is to evaluate the effect of perioperative tamsulosin for the reduction of POUR in men, as well as the impact on the interventions and hospital admissions related to this complication.