INTRODUCTION: Preoperative polymicrobial urine cultures are common, but the associated risk of nosocomial infection is currently unknown. We aimed to analyze the risk of postoperative infection in patients with preoperative polymicrobial urine cultures. METHODS: This was a prospective cohort study conducted from November 2018 to October 2020. Polymicrobial urine cultures were defined by at least the presence of 3 bacteria without leukocyturia threshold on two consecutive samples in the month preceding the surgical procedure. Data on postoperative infections were collected during hospitalization until day 30. A postoperative infection was defined by the occurrence of clinical signs (fever, chills, and suppurated process on the surgical site) associated with the prescription of an antibiotic therapy. RESULTS: Sixty-eight patients were included, and seven developed a postoperative infection with a microbe identified in blood or urine cultures. There was a significant association between leukocyturia ≥104 (p = 0.02) and the administration of intraoperative antibiotic prophylaxis (p < 0.001). In contrast, there was no significant association between postoperative infections for patients with polymicrobial preoperative urine cultures and having received or not an empirical antibiotic therapy. CONCLUSION: The rate of postoperative infection in patients with polymicrobial urine culture before urological procedure was 10.2%. Further studies are needed to assess the antibiotic prophylaxis to be used in this situation.