Objective: To report microbial pathogens detected at infection-related readmissions, including their susceptibility to antimicrobials. Materials and Methods: A retrospective review of 785 patients who underwent radical cystectomy for bladder cancer at a tertiary center in Denmark between 2009 and 2019. All patients received prophylactic cefuroxime preoperatively and pivmecillinam at stent- or catheter removal. Data were collected through the national medical records and microbiology database. The primary outcome was readmission rate and pathogens detected at infection-related readmissions. Univariable and multivariable regression analyses were carried out to identify risk factors of readmission. Results: Within 90 days of surgery, 225 (29%) patients experienced at least one infection-related readmission. The most common pathogen identified was Enterococcus spp (24% of all positive samples). In blood cultures, the most dominant species were Escherichia coli (29%) and Staphylococcus spp (26%). Due to the heterogeneity in microbial species identified, more than one-third of the bacteria where mecillinam was tested showed resistance. Most isolates were susceptible to piperacillin + tazobactam. Orthotopic neobladder and continent cutaneous reservoir were associated with the highest risk of infection-related readmission compared to ileal conduit (odds ratios 2.78 [95%CI 1.66;4.65] and 3.08 [95%CI 1.58;5.98], respectively). Patients with diabetes had an increased risk of infection-related readmission compared to patients without diabetes (odds ratio 1.67 [95%CI 1.02;2.73]). Conclusion: Nearly one-third of all patients experienced at least one postoperative infection-related readmission with a wide range of microbial etiologies. Generalizability of our results is uncertain, but the data can be used to plan interventional trials of antibiotic prophylaxis.