Complicated urinary tract infection (UTI) is associated with a condition [eg structural or functional abnormalities of the genitourinary tract (GUT)] or the presence of an underlying disease that interferes with host defense mechanisms, which increases the risks of acquiring infection, failing therapy or having recurrent infections. The successful treatment of a complicated UTI considers effective antimicrobial therapy, optimal management of the underlying abnormalities or other diseases and adequate life-supporting measures.