BACKGROUND: National quality initiatives have mandated the earlier removal of urinary catheters after surgery to decrease urinary tract infection rates. A potential unintended consequence is an increased postoperative urinary retention rate. OBJECTIVE: The aim of this study was to determine the incidence and risk factors for postoperative urinary retention after colorectal surgery. DESIGN: This was a prospective observational study. SETTINGS: A colorectal unit within a single institution was the setting for this study. PATIENTS: Adults undergoing elective colorectal operations were included. INTERVENTIONS: Urinary catheters were removed on postoperative day 1 for patients undergoing abdominal operations, and on day 3 for patients undergoing pelvic operations. Postvoid residual and retention volumes were measured. MAIN OUTCOME MEASURES: The primary outcomes measured were urinary retention and urinary tract infection. RESULTS: The overall urinary retention rate was 22.4% (22.8% in the abdominal group, 21.9% in the pelvic group) and was associated with longer operative time and increased perioperative fluid administration. Mean operative time for those with retention was 2.8 hours and, for those without retention, the mean operative time 2.2 hours (abdominal group 2 hours vs 1.4 hours, pelvic group 3.9 hours vs 3.1 hours, p ≤ 0.02). Patients with retention received a mean of 2.7L during the operation, whereas patients without retention received 1.8L (abdominal group 1.9L vs 1.4L, pelvic group 3.6L vs 2.2L, p < 0.01). In the abdominal group, patients with and without retention also received different fluid volumes on postoperative days 1 (2.2L vs 1.7L, p = 0.004) and 2 (1.6L vs 1L, p = 0.05). Laparoscopic abdominal group had a 40% retention rate in comparison with 12% in the open abdominal group (p = 0.004). Age, sex, preoperative radiation therapy, preoperative prostatism, preoperative diagnosis, and level of anastomosis were not associated with retention. The urinary tract infection rate was 4.9%. LIMITATION: The lack of documentation of preoperative urinary function was a limitation of this study. CONCLUSIONS: The practice of earlier urinary catheter removal must be balanced with operative time and fluid volume to avoid high urinary retention rates. Also important is increased vigilance for the early detection of retention.