Clinical features of urinary tract infections in the elderly are well defined but primarily based on data obtained from female subjects. The pathophysiology of urinary tract infections in men is less well characterized. Recent epidemiologic investigations highlight the nearly identical prevalence of bacteriuria in elderly men and women, but women are more frequently persistently bacteriuric with high urinary titers ofEscherichia coli. Sex and age define clinically and bacteriologically distinct populations with serious urinary tract infections. Risk factors for infection may include age-related increases in prevalence of incontinence, onset of nosocomial diarrhea in patients with urinary catheters, and groin skin carriage of Proteeae species. Quinolone antibiotics are useful in the elderly but might interact adversely with concurrently used medications.