In urinary catheterization, a urinary catheter,like foley catheter, a slender plastic tube, is pushed up a patient's urinary tract into their bladder. A balloon located at the end of the catheter is then usually inflated with saline solution to prevent the catheter from slipping out. In males, this tube is inserted into the urinary tract through the penis. Urine passes through the tube, and into a plastic bag.

Common indications to catheterize a patient include urinary retention (acute or chronic) and any indication to accurately measure urinary output (for example, in cardiac patients undergoing diuretic treatment).

Patients undergoing major surgery are often catheterized, and may remain so for some time after the surgery.

In some situations, incontinent patients are catheterized to reduce their cost of care, but this is not recommended because chronic catherization carries a significant risk of a urinary tract infection.

For many patients the insertion and removal of a catheter can cause severe pain to the client so a topical anesthetic can be used to alleviate most pain.

Catherization should be performed as a sterile medical procedure and should only be done by trained, qualified personnel, using equipment designed for this purpose.