Urinary tract infections (UTIs) are the most common infections seen in the hospital setting, and the second most common infections seen in the general population. Due to women's anatomy, UTIs are especially problematic for them, and up to one-third of all women will experience a UTI at some point during their lifetimes. Appropriate treatment of a UTI requires accurate classification that includes infection site, complexity of the infection, and the likelihood of recurrence. The predominant pathogen in both complicated and uncomplicated UTI remains pathogenic Escherichia coli, although Klebsiella sp. and Proteus appear with increased frequency in complicated UTI. Most often, bacteria cause UTIs by ascending means through the urethra into the bladder. Bacteria must possess virulence factors to cause UTI. Host defense factors that predispose patients to UTI include urinary stasis, abnormal urinary tract anatomy, diabetes mellitus, debility, and aging. Estrogen-related issues and short urethras predispose women to UTI. Although urine culture, with >105 colony-forming units/mL (CFU/mL) in symptomatic patients, remains the diagnostic "gold standard," correlation of the patient's history and physical examination with urinalysis (including nitrite dipstick and leukocyte esterase test) results usually suffices to diagnose UTI. Three-day of antimicrobial treatment is recommended for simple cystitis. Acute pyelonephritis, an infection of the kidney parenchyma tissue, is treated with antibiotics for 7 to 14 days depending on the antimicrobial agent used and the severity of infection. In addition, patient classification determines the need for hospitalization or for urological imaging studies. Women with recurrent UTIs merit consideration for antimicrobial prophylaxis. Self-administered topical vaginal estradiol cream is an important adjunct in UTI prevention for postmenopausal women. Asymptomatic bacteruria only merits antimicrobial therapy in high-risk patients or those colonized with Proteus species.