 This is a pro- and retrospective cohort study to evaluate the natural history and outcome of various treatment options of patients with fistula. At each clinical visit parameters describing activity of a fistula, potential underlying Crohns disease, investigations as well as the current treatment will be entered into a database. Selected patients can also be contacted by phone in the form of a structured interview. Data will be analyzed to determine treatment outcomes, characterize the natural history as well as risk factors for complications of treatment and an unfavorable disease course. The same data will be obtained and analyzed retrospectively from patients who visited the clinic prior to January 2017. 