Background: Transrectal ultrasound guided biopsies (TRUSp) are associated with a risk of serious infections. Recently, there has been a rise in incidence of infections after TRUSp and quinolone-resistant bacteria. The most commonly used prophylaxis is ciprofloxacin (CFLX). Objective: To document the incidence and risk factors of post-TRUSp infections and investigate the microbial resistance patterns for the patients presenting with a serious infection after TRUSp. Materials and methods: Data were collected, including age, comorbidity, previous TRUSp, number of biopsies, previously received antibiotics, time between TRUSp and hospitalization, results of microbiological cultivations, antibiotic prophylaxis, and development of infection for all patients at The University Hospital of Southern Denmark, Esbjerg who underwent TRUSp from November 2014 to November 2016. Results: In total, 590 patients were included and 37 (6.1%) patients were hospitalized with symptoms of infection. Of those 37 patients, 21 (56,8%) patients had positive microbiology (blood and/or urine), 18 (48.6%) patients were infected with E. coli and 11 (29.7%) patients had CFLX-resistant E. coli. If patients had previously received antibiotics, they had a significantly higher risk of developing infection after TRUSp (p = 0.01). Conclusion: Patients who have been exposed to antibiotics before TRUSp are at higher risk of developing serious infections as a complication to TRUSp. CFLX-resistant E. coli were a major reason for hospitalization.