An accumulation of urine in the bladder due to an abrupt inability to empty the bladder. It occurs most often in men over age 60, and is often the result of benign prostatic hyperplasia. It is the most common urologic emergency.

Causes
- Any process that causes increased bladder-outlet resistance or decreases bladder contractility
- Benign prostatic hyperplasia
- Side effects of drugs
- Fecal impaction
- Prostatic cancer
- Acute prostatitis
- Neurogenic bladder
- Urethral stricture or stone
- Impingement on sacral nerves by protruding intervertebral disk
- Spinal cord injury

History
- Strong urge to void but inability to do so
- Suprapubic fullness and pain
- Voiding habits before retention (hesitancy, dribbling, daytime frequency, nocturia)
- Bowel habits, last bowel movement and its consistency
- Drugs (alcohol, sedatives, decongestants in over-the-counter cold remedies, anticholinergics, antipsychotics, and antidepressants)

Physical findings
- Pulse may be elevated
- Patient may appear in moderate-to-acute distress (but there may be no evidence of distress with a neurogenic bladder)
- Patient may be restless and sweaty
- Bladder distension may be noted on abdominal inspection
- Tender, distended bladder may be felt above symphysis, often reaching umbilicus (neurogenic bladder is distended but non-tender)
- Rectal examination: fecal impaction, enlargement of prostate, nodular or rocky hard prostate, decreased anal tone, or absent perineal sensation may be present

See reference for details.

Adapted from Health Canada. First Nations & Inuit Health. Adult Care - Chapter 6 - Genitourinary System. Internet. Accessed on January 28, 2016.