We report the clinical and radiologic features of 12 patients with acute intestinal anisakiasis. Diagnosis of anisakiasis was made immunologically by positive antibody to Anisakis larvae and a recent history of raw fish intake. Severe abdominal pain was a major symptom in these patients-half experienced fluid levels indicating ileus on plain x-ray films of the abdomen. Radiologic findings included irregular thickening of the jejunum, ileum, or colon, with mucosal edema and luminal narrowing with dilatation of the proximal intestine. In two cases a thread-like filling defect suggesting a worm was visualized on the x-ray film. These findings were interpreted as anisakiasis. Although ileus developed in some patients, all were treated and cured completely without surgery.