Increase of antibiotic resistance jeopardizes the effectiveness of empirical antibiotic therapy of urinary tract infections (UTI). The aim of this study was to estimate the frequency of UTI causative agents in relation to the UTI category and to investigate the resistance rates in the most frequent uropathogens. The influence of the UTI category on the frequency and sensitivity pattern of uropathogens was investigated among inpatients and outpatients of the University Hospital for Infectious Diseases, Zagreb. Escherichia coli was the most frequent causative agent in every UTI category. The lowest rate of E. coli was recorded among outpatients treated for complicated and recurrent UTI. These patients had significantly higher rate of enterococci. Statistically significant difference (p < 0.05) in E. coli resistance rates among different UTI categories was found for co-trimoxazole (p = 0.007) and cephalexin (p = 0.042), while differences for ciprofloxacin and norfloxacin demonstrated borderline values (p = 0.063).