The radiologic and endoscopic findings in six patients with anisakiasis of the colon were analyzed. The diagnosis was based on the demonstration of Anisakis larvae at radiography or on elevated serum levels of antibodies to this parasite. All patients reported abdominal symptoms 12-23 hours after the ingestion of raw fish. Double-contrast barium enema examination, performed 2-4 days after the onset of syptoms in all the patients, revealed that the right side of the colon was frequently affected by edema, which was radiographically demonstrated as luminal narrowing and thumbprinting. In addition, the worm was shown at radiography in four patients. Colonoscopy, performed 1-7 days after the onset of symptoms, revealed edematous mucosa, characterized by narrowing and multiple smooth and round protrusions, in all four of the patients studied, but it failed to demonstrate the worm in any patient. The authors believe that the demonstration of these features, together with a history of raw fish ingestion, is essential for the diagnosis of this disorder.