Anal fistulae do not heal spontaneously without surgery. Knowledge of anorectal anatomy and function, and diligent examination frequently requiring anaesthesia are prerequisites for adequate assessment, classification and treatment of the pathology. Fistulography, endoanal ultrasound and MRI of the anorectum may have additional diagnostic value with therapeutic impact in complex and recurrent fistulae. Parks' classification is most useful because it is the best guide for surgical therapy. In the modern treatment of trans- or suprasphincteric fistula in ano fast or slow division of any part of the striated perianal musculature is to be avoided in order to prevent anal incontinence.