Fistulas in Crohn's disease are classified as internal fistulas, for example, enteroenteric, enterovesical, rectovaginal, and external fistulas, for example, enterocutaneous, perianal, and parastomal. Although radiographic contrast studies are superior to endoscopy for diagnosing fistulas, endoscopic procedures have a definite role in the evaluation and management of fistulizing Crohn's disease. Endoscopy allows for tissue sampling, and provides information regarding the extent and severity of gastrointestinal inflammation, and the presence of such complications as strictures and cancer. Preoperative colonoscopy has particular value in assessing an enterocolonic fistula, and has important implications regarding the type of surgery performed. Endoscopic therapy for Crohn's fistula is less certain, but may allow for dilation of associated strictures, and may someday serve as a better delivery system for targeted anticytokine and immunologically based therapy.