Urinary tract infections (UTIs), including cystitis and pyelonephritis, are common. Each year, they account for more than 10 million outpatient visits and more than 3 million emergency department visits. Recurrent UTIs (defined as three in 1 year or two in 6 months) also are common, occurring in 20% to 30% of women. The annual incidence of UTIs is 12.1% among women and 3% among men. Cystitis symptoms include lower abdominal pain, dysuria, and urinary urgency or frequency. Escherichia coli is the most common pathogen. Cystitis often is diagnosed inappropriately when patients have asymptomatic bacteriuria (ie, positive urine culture result without symptoms). This can result in unnecessary antibiotic therapy. For uncomplicated acute cystitis in women, guidelines recommend nitrofurantoin for 5 days, trimethoprim-sulfamethoxazole for 3 days (if local drug-resistance rates are less than 20%), fosfomycin in a single dose, or pivmecillinam for 5 days. Effective prophylactic options for UTI include antibiotics and vaginal estrogen for postmenopausal women. Antibiotics are most effective but are associated with a risk of increased drug resistance. Patients with pyelonephritis present with costovertebral tenderness, fever, and urinary symptoms. Third-generation cephalosporins are preferred for management. Significant complications of pyelonephritis include sepsis or septic shock, obstructive pyelonephritis, emphysematous pyelonephritis, perinephric abscess, and kidney transplant rejection. For pregnant patients with pyelonephritis, hospitalization and intravenous antibiotics are indicated.