AbstractResearch has demonstrated that systematic preoperative oral hygiene reduces nosocomial infections after elective thoracic surgery. However, the impact of preoperative oral hygiene on patients undergoing urologic procedures is unknown. Therefore, the aim of this study was to investigate the effects of systematic preoperative oral hygiene on prescriptions with antibiotics following cystectomy or urethroplasty. A quasi‐experimental study design included all patients undergoing elective radical cystectomy or urethroplasty from 1 January 2018 to 31 May 2021. Patients undergoing cystectomy or urethroplasty were grouped into a prospective intervention group and a retrospective control group. Patients in the intervention group were admitted from 1 January 2020 to 31 May 2021, and were recommended to brush their teeth and rinse their mouths with chlorhexidine gluconate 0.12% four times a day starting 2 days before surgery and continuing until the morning of the operation. Patients admitted from 1 January 2018 to 31 December 2019 received no oral hygiene recommendations and were used as a retrospective control group. Data on oral hygiene performance were self‐reported and collected at admission and data on prescription of antibiotics were collected through the patients' records. The relative risk was calculated to report the effect of the intervention. In total, 39 patients with cystectomy were in the intervention group, whereas 31 were in the control group. For patients having urethroplasty, 27 were in the intervention group and 98 were in the control group. The effect of oral hygiene on the prescription of antibiotics for patients who completely adhered to the oral hygiene recommendations showed a relative risk of 0.554 (95% CI 0.333–0.921) p = 0.02 for cystectomy and 0.825 (95% 0.308–2.209) p = 0.70 for urethroplasty. This study showed a statistically significant reduction in the prescription of antibiotics following oral hygiene recommendations for patients undergoing cystectomy. However, no statistically significant effect was demonstrated for patients undergoing urethroplasty. Despite this result, it seems important to be aware of oral hygiene in patients undergoing surgery to potentially reduce the number of infections and the use of antibiotics because of the antimicrobial resistance that the healthcare system faces.