Urinary tract infection (UTI) is the most common infectious complication following renal transplantation. The purposes of this study were to determine the causative agents of UTIs among renal transplant recipients and to compare the antibiotic susceptibilities of Escherichia coli strains isolated from renal transplant recipients and complicated community-acquired UTIs. We evaluated 75 episodes of 63 recipients with confirmed UTI who underwent transplantation during the period 1981 to 2006 at our center. Medical records of the patients were reviewed retrospectively. To compare the susceptibility rates of E coli, 226 isolates from nontransplant patients with complicated community-acquired UTIs were also evaluated. Ten episodes (13.3%) occurred in the first month following the transplantation, 11 (14.7%) in the period of the second month to the sixth month, and 54 (72%) after the sixth month of transplantation. Forty-six (61.3%) isolates were E coli. Among these isolates, ciprofloxacin resistance rates were 50% (2/4) in the first month after transplantation, 75% (6/8) in the period of the second month to the sixth month, and 32.4% (11/34) beyond 6 months after transplantation. The resistance rates of trimethoprim/sulfamethoxazole (TMP-SMX) in the same time periods were 100% (4/4), 87.5% (7/8), and 70.6% (24/34), respectively. The rates of resistance to TMP-SMX among E coli isolated from renal recipients were significantly higher than those in community-acquired complicated UTIs. The increased resistance of urinary pathogens to this agent is a major concern. Although high resistance rates of ciprofloxacin against E coli strains were determined in this group, it was not found to be statistically significant.