Magnetic resonance imaging (MRI) depicts infectious foci in the perianal region better than any other imaging modality. MRI allows definition of the fistula, associated abscess formation and its secondary extensions. Accurate information is necessary for surgical treatment and to obtain a decrease in the incidence of recurrence and complications. Radiologists should be familiar with anatomical and pathological findings of perianal fistulas and classify them using the MRI - based grading system. The purpose of this article was to provide an overview for evaluation of perianal fistulas, examples of various fistula types and their classification.