Urine retention, a potentially life-threatening condition, may result from neurologic or psychological disorders or obstruction of urine flow. Medications such as anticholinergics, antihistamines, and antidepressants may also cause urine retention. Traditionally, the amount of urine retained in the bladder was measured by urinary catheterization, placing the patient at risk for infection. Noninvasive bladder ultrasonography provides an assessment of bladder volume while lowering the risk of urinary tract infection.