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Foley catheters are flexible (usually latex) tubes that are passed through the urethra during urinary catheterization and into the bladder to drain urine. They are retained by means of a balloon at the tip which is inflated with sterile water. The balloons typically come in two different sizes 5 cc and 30 cc.

The relative size of a Foley catheter is described using French units (F). The most common Foley catheters typically range from 10 F - 28 F. 1 F is equivalent to 0.33 mm = .013" = 1/77" of diameter. [1] Thus the size in French units is roughly equal to the circumference of the catheter in millimetres.

Foley catheters come in several sub-types. Coudé (French for elbowed) catheters have a 45° bend at the tip to allow easier passage through an enlarged prostate. Council tip catheters have a small hole at the tip which allows them to be passed over a wire. 3-way catheters are used primarily after bladder, prostate cancer or prostate surgery. They have a third arm or bell that allows an irrigant to pass to the tip of the catheter through a small separate channel into the bladder. This serves to wash away blood and small clots through the primary arm that drains into a collection device. This prevents larger clots, that might plug the catheter, from forming. The second or inflation arm has a small plastic valve that allows for the introduction or removal of sterile water through a very small channel to inflate or deflate the retaining balloon.

They can also be used to "ripen" the cervix, to allow the induction of labour. The catheter is inserted behind the cervical wall and inflated. The remaining length of the catheter is gently pulled and taped to the inside of the woman's leg. The inflated balloon applies pressure to the cervix, like the baby's head would prior to labour, causing it to dilate. Over time the catheter is adjusted and re-taped to maintain pressure on the cervix. When the cervix has dilated sufficiently, the catheter simply drops out.

They were designed by Dr. Frederick Foley, a surgeon working in Boston, Massachusetts in the 1930s, when he was a medical student.

His original design was adopted by C R Bard of Murray Hill, New Jersey, who manufactured the first prototypes and named them in honour of the surgeon.

There is concern that additives and plasticizers (such as phthalates) used in vinyl (polyvinyl chloride - PVC) catheters may leach out of plastic (vinyl) catheters. Catheters are meant to be placed into the body, possibly for extended periods of time. As a result, any potentially harmful leaching of chemicals is of particular concern. Rubber (latex) catheters are available, but may not be acceptable for individuals who have latex sensitivities or allergies. Silicone catheters are available and may prove to be the safest but typically are more expensive than rubber or vinyl catheters. Silicone coated vinyl catheters are available, but are not suggested for long term use. For more information, see the entry on polyvinyl chloride safety.

Foley catheters made from latex will become colonised with bacteria quickly, allowing urinary tract infection within 4 days, whereas all silicone Foley catheters can remain in situ for up to 6 weeks before changing or removal.