Urinary tract infections (UTIs) are the most common infections in renal transplant recipients (RTR). Klebsiella spp is a well-recognized source of nosocomial infections in immunocompromised patients and is also the most common pathogen capable of producing extended-spectrum β-lactamases (ESBLs).We performed a retrospective cohort study reviewing medical records of patients followed-up at Gdańsk Transplantation Centre. We analyzed urine cultures performed within the first 12 months after renal transplantation (RT) with reference to clinical data. We recorded all Klebsiella spp UTIs.We studied urine cultures and clinical data from 335 RTRs. We observed 59 Klebsiella spp episodes in 24 RT patients, including 10 cases of acute graft pyelonephritis and 8 of urosepsis. More than half were caused by ESBL+, whereas there were no carbapenemase-producing strains. Almost 80% of episodes were diagnosed beginning from the second month post-transplantation. More than 60% of upper Klebsiella spp UTIs were due to ESBL+ strains, although we did not identify any host risk factors including vesico-ureteral reflux, strictures at the uretero-vesical junction, history of recurrent UTIs before RT, comorbidity measured by Charlson Comorbidity Index, history of acute rejection, use of induction, and type of immunosuppression used. Upper Klebsiella spp UTIs were slightly more prevalent in males with urinary flow impairment due to various reasons.Klebsiella spp virulence factors, not the host factors, seem to be mostly responsible for developing upper UTIs in RT patients.