Normally, urine in the bladder and the urinary tract from kidney to the last third of the urethra is sterile. When the urinary tract becomes infected with bacteria, an inflammation at the site of infection results in symptoms of urinary tract infection (UTI), and significant numbers of bacteria and white blood cells (WBC) appear in the urine. This paper describes how, by the examination of urine, the clinical microbiology laboratory contributes to the diagnosis, monitoring and treatment of UTI.