Urinary tract infections are a frequent problem in ambulatory practices. According to the localization of the infection and to complicating factors we differentiate between various syndromes with different clinical presentations. Relevant diagnostic criteria are a bacteriuria of greater than or equal to 100 organisms par millilitre or a pyuria of greater than or equal to 5 leukocytes per high power field. For acute cystitis, a treatment for three days is recommended. Cotrimoxazole or quinolones are effective drugs, which are more and more recommended for the treatment of acute pyelonephritis, too.