Urinary tract infections remain the most common type of bacterial infections in adults. The last decade has clarified their aetiology and shown that adherence of Gram-negative bacteria to epithelial cells in the urinary tract is a major virulence factor. Recent studies have confirmed the clinical importance of such adhesion. Several studies have demonstrated increasing resistance problems in bacterial species causing urinary tract infections. This has especially been the case for beta-lactam antibiotics and older drugs such as co-trimoxazole. The fluoroquinolones remain effective in most parts of the world and seem superior to beta-lactams for the treatment of all types of urinary tract infection. Their use should be restricted as much as possible, however, to prevent emergence of resistance.