Fistula-in-ano describes an abnormal communication between the anal or rectal epithelium and the perianal skin. Patients present with a range of symptoms and findings ranging from intermittent discharge, pain, and swelling, to acute sepsis. Treatment is surgical, but postsurgical recurrence is not uncommon. Recurrence is frequently due to a part of the tract remaining undetected, and thus untreated, at the initial surgery. Radiological investigation aims to demonstrate clinically undetected infection and fistulous tracts in order to assist presurgical planning and ultimately reduce recurrence rates. This article discusses relevant anatomy and fistula pathogenesis, before focusing on the roles and utilization of the two common modalities, anal endosonography (AES) and magnetic resonance imaging (MRI), in the preoperative workup of fistula-in-ano.