Pasteurella pseudotuberculosis infection of the intestine produces a syndrome that simulates acute appendicitis. Prodromal malaise and anorexia, abdominal pain and tenderness localized in the right lower quadrant, fever, and leukocytosis are characteristics of the disease. In the typical patient, enlarged mesenteric lymph nodes are found at operation. The distal ileum may be thickened and edematous. Histologic sections show ulceration of the ileal mucosa and microabscesses within submucosal and lymph node germinal centers. Clinically, the disease may be distinguished from appendicitis by a test for agglutinating serum antibodies. Although a large number of cases in Europe have been reported, there have been no reports of Pasteurella pseudotuberculosis infection of human beings in the United States. Three such patients, all living in California, are reported with a description of the clinical and anatomic findings.