A fistula is an abnormal channel that connects one organ to another, causing the flow of fluids in an organ where they do not belong. The fluid may be normally present in the body, but it can be pathological, as in the case of an abscess fistula. Removal can be done inside or outside the body. Only the knowledge of the path of the fistula enables the proper treatment and accurate evaluation of the impact on the body. The most common fistulas are located at the anus, the digestive tract, or urinary system. The term fistula is also used for treatment, when performing an arteriovenous fistula, the method for connecting an artery and a vein, and is mostly used in hemodialysis.