Rational antibiotic therapy of urinary tract infections Urinary tract infections (UTI) are frequent infections in the outpatient and nosocomial setting. Generally UTI can be stratified into uncomplicated and complicated infections with respect to treatment options. Uncomplicated UTI are mainly caused by E. coli, whereas complicated UTI exhibit a broader bacterial spectrum with a higher rate of multiresistant uropathogens. On the other hand increasing resistance rates are also found in uncomplicated UTI, e.g. against aminopenicillins, Co-trimoxazol and increasingly also fluoroquinolones. This fact has to be considered in the empirical therapy. Recurrent UTI are frequently found in young, sexually active women, and postmenopausal women. In complicated UTI the complicating factors have to be diagnosed and treated additionally to the antibiotic treatment. If not treated, a severe UTI and urosepsis can develop.