Introduction: Acute appendicitis is the most common emergency abdominal operation. One of its different pathogenesis is infection with microbial agents such as Yersinia. Yersinia is the most common cause of mesenteric adenitis and may represent with right lower quadrant abdominal pain and tenderness and sometimes with systemic manifestation. Frequently in patient with Yersinia infection appendix is normal but may be involved as acute appendicitis.

Case Report: This case report represent a 12 years old girl with acute appendicitis and mesenteric adenitis secondary to underline infections process (high probably Yersinia according to clinical syndrome ) with multiple organ involvement .

Conclusion: We conclude that in patients with clinical findings of acute appendicitis and without improvement after surgery, it should be considered an underline other disease process such as appendicitis and mesenteric adenitis with Yersinia infection.