Urinary retention can be either acute or chronic. The most common cause of retention is outlet obstruction secondary to benign prostatic hypertrophy in men although medication use, acute neurologic dysfunction, urinary tract bleeding or calculi, and other anatomic obstruction are also common causes in both sexes. Acute syndromes typically present with rapid onset of lower abdominal pain occasionally radiating to the lower back. Patients typically complain of difficulty voiding but some may not volunteer this information. Chronic obstruction usually presents with lower abdominal pain and the patient may note incomplete voiding or the need to void frequently.