Background: The purpose of this study was to evaluate the efficacy of tamsulosin, administered preoperatively, for the prevention of postoperative urinary retention (POUR). POUR is a common complication of abdominal surgery, leading to the use of urinary catheters, which are a risk factor for urinary tract infection. Tamsulosin is a uroselective alpha-1a blocker used for the treatment of lower urinary tract symptoms. Materials and methods: A randomized, double-blind, placebo-controlled trial was undertaken from August 2015 to May 2018. Adults undergoing elective inpatient abdominal surgery were randomized to receive either tamsulosin 0.4 mg or placebo daily for 7 d before surgery and continuing for up to 7 d postoperatively. The primary outcome was need for at least a single intermittent catheterization postoperatively. Secondary outcomes included first postvoid residual volume, number of catheterizations, need for replacement of an indwelling catheter, hospital length of stay, and urinary tract infection within 30 d of surgery. Results: A total of 158 participants were enrolled, with a final analytic cohort of 141 participants. The two groups had similar baseline characteristics, operative characteristics, and timing of catheter removal. There was no difference in the incidence of POUR between the two groups (26% in tamsulosin versus 31% in placebo, P = 0.49). There was also no difference in any of the secondary outcomes between the two groups. Epidural usage, open surgery, and age <50 were identified as risk factors for POUR. Conclusions: Perioperative prophylaxis with tamsulosin is not effective in reducing the incidence of POUR in patients undergoing elective abdominal surgery.