In medicine, a catheter is a tube that a health professional may insert into part of the body. The process of inserting a catheter is catheterization. In most uses it is a thin, flexible tube: a "soft" catheter; in some, it is a larger, solid tube: a "hard" catheter.

Placement of a catheter into a particular part of the body may allow:

• draining urine from the urinary bladder as in urinary catheterization, i.e. Foley Catheter or even when the urethra is damaged as in super-pubic catheterization .
• administration of intravenous fluids , medication or parenteral nutrition
• angioplasty
• injection of dye or radio-opaque contrast into blood vessels or other structures to visualize abnormalities , as in cardiac catheterization, which is part of coronary angiography
• direct measurement of blood pressure in a artery or vein
• infusion of local anesthetics and other drugs for epidural anesthesia
• suctioning of unwanted fluids from the airway (with a hard catheter)
• Administration of a lethal injection

A central line is a conduit for giving drugs or fluids into a large-bore catheter positioned either in a vein near the heart or just inside the atrium.

See also:

• cannula
• stent