Participants will be recruited consecutively during their preoperative visit to the outpatient clinic. Participants will be followed by a logbook throughout the follow-up period, as well as by their surgical and research teams. Follow-up will begin on the first day of pre-operative medication and will end 30 days after surgery. Patients randomized to the intervention group will receive 0.4 mg tamsulosin capsules, administered orally, once a day for 5 days before surgery, the morning of surgery and the day after surgery. Patients assigned to the placebo group will receive glucose capsules according to the same protocol. The glucose capsules will be manufactured by the pharmacy of the CHU de Quebec. All patients will have a foley catheter inserted for surgery. Their urinary catheter (foley catheter) will be removed at 6:00 AM the day after their surgery (post-operative day 1). The diagnosis of urinary retention will be suspected by a member of the patient's medical team if a patient has no miction for 8 hours or more or 4 hours or more after removal of foley catheter or after the surgery. In these cases, a portable bladder scanner will be used. The diagnosis of post-operative urinary retention (POUR) will be confirmed in two situations: 1. If there is 500ml of urine or more in the bladder 2. If there is 300ml or urine or more with at least 1 of the following symptoms: urge to urinate with inability to urinate, suprapubic pain or signs and symptoms of delirium. When the diagnosis of POUR will be made, urine will be removed from the bladder using an in/out bladder catheterization. After using a bladder catheterization, a portable bladder scanner will be used again if a patient has no spontaneous urination for the first 4 hours after catheterization. A second bladder catheterization will be done once again in the same two situations as described above. At the third bladder catheterization, a urinary (foley) catheter will be inserted. The catheter will be left in place for 24h before attempting a trial of void. A member of the medical team will then collect the information in the patient's logbook and medical record. Adherence to drug intake will be self-reported to the patient's diary. The patient can indicate why he missed one or more doses of the drug. Patients will receive a list of potential side effects of tamsulosin with their logbook. The side effects will be self-reported by the patient to the logbook each day. The patients' logbook will be analysed by the research team. Two independent reviewers of the research team will collect the other variables. They will perform a standardized retrospective revision of the medical records according to a pre-established data collection grid. We will perform an intention-to-treat analysis in this prospective randomized study. Postoperative urinary retention remains a frequent complication and causes significant discomfort in men undergoing rectal resection. The decrease in its incidence could then significantly reduce the number of bladder catheterizations required postoperatively, and thus reduce the incidence of complications associated with it. The prevention of POUR will allow patients a more harmonious postoperative recovery, limited in inconvenience and side effects, and an earlier return home. Ultimately, the health care costs associated with this postoperative complication may be reduced.