A pin-size opening near the anus with recurrent pain and discharge is a fistula-in-ano. The internal opening is first sought clinically: PR examination (indurated tract) and proctoscopy, which may show the internal opening, guided by Goodsall's rule. The lecture says that if examination is inconclusive, an anoscope is used, not MRI. MRI, endo-anal US and fistulography are kept for recurrent or complex fistulas.