PURPOSE: The administration of antimicrobial prophylaxis for postoperative urinary tract infections following transurethral resection of bladder tumors is controversial. We aimed to systematically review evidence on the potential effect of antimicrobial prophylaxis on postoperative urinary tract infections and asymptomatic bacteriuria. MATERIALS AND METHODS: We conducted a systematic search in Embase®, Medline® and the Cochrane Central Register of Controlled Trials. Randomized controlled trials and nonrandomized controlled trials assessing the effect of any form of antimicrobial prophylaxis in patients with transurethral resection of bladder tumors on postoperative urinary tract infections or asymptomatic bacteriuria were included. Risk of bias was assessed using RoB 2.0 or the Newcastle-Ottawa Scale. Fixed and random effects meta-analyses were conducted. As a potential basis for a scoping review, we exploratorily searched Medline for risk factors for urinary tract infections after transurethral resection of bladder tumors. The protocol was registered on PROSPERO (CRD42019131733). RESULTS: Of 986 screened publications, 7 studies with 1,725 participants were included; the reported effect sizes varied considerably. We found no significant effect of antimicrobial prophylaxis on urinary tract infections: the pooled odds ratio of the random effects model was 1.55 (95% CI 0.73-3.31). The random effects meta-analysis examining the effect of antimicrobial prophylaxis on asymptomatic bacteriuria showed an OR of 0.43 (0.18-1.04). Risk of bias was moderate. Our exploratory search identified 3 studies reporting age, preoperative pelvic radiation, preoperative hospital stay, duration of operation, tumor size, preoperative asymptomatic bacteriuria and pyuria as risk factors for urinary tract infections following transurethral resection of bladder tumors. CONCLUSIONS: We observed insufficient evidence supporting routine antimicrobial prophylaxis in patients undergoing transurethral resection of bladder tumors for the prevention of postoperative urinary tract infections; our findings may inform harmonization of international guidelines.