Acute urinary tract infection is a major health problem among women, accounting for considerable morbidity and health care costs. We review recent developments in the diagnosis and treatment of these infections. In acute lower urinary tract infection, empiric short-course therapy (single-dose or 3-day therapy) with one of several antibiotics is recommended in the absence of complicating factors. When complicating factors are present, the antibiotic susceptibility profile of the infecting organism should be determined and therapy with an appropriate agent should be provided for 7 days. Ampicillin and related drugs are probably inferior to trimethoprim-sulfamethoxazole in the treatment of occult renal infection. In acute pyelonephritis, most patients require hospitalization and treatment with intravenous antibiotics until they can take oral medications. In uncomplicated cases, a single broad-spectrum intravenous agent can be used initially, followed by an oral agent selected on the basis of antibiotic-susceptibility testing results. Patients with uncomplicated acute pyelonephritis who are less ill can be managed with oral therapy as outpatients, again with reference to the results of antibiotic-susceptibility testing. Complicated acute pyelonephritis requires more aggressive diagnostic and therapeutic measures. Therapy for uncomplicated acute pyelonephritis should be given for 14 days. The role of post-therapy cultures in the management of urinary tract infection is not well defined, but cultures probably can be safely omitted in most cases of uncomplicated acute cystitis.