Appendix metastasis from lung adenocarcinoma is very rare. Metastasis-induced acute appendicitis is extremely rare. We present the case of a 77-year-old woman with stage IV lung adenocarcinoma who presented with acute appendicitis. She was admitted to the emergency department with complaints of right lower quadrant pain, nausea and vomiting for 12 hours. Contrast-enhanced abdominal computed tomography showed a dilated appendix with a thickened wall suggestive of acute appendicitis. She underwent appendectomy, and the pathological examination of the appendiceal specimen demonstrated metastatic poorly differentiated adenocarcinoma from the lung. After treatment for acute appendicitis, she was discharged and recovered uneventfully, and was then referred to our thoracic oncology department to resume treatment for her lung cancer.