Appendix agenesis is rarely seen, even for many experienced surgeons. The incidence of appendix agenesis has been reported as 1 per 100,000 cases admitted for surgery with a diagnosis of acute appendicitis. A 20-year old male with no history of surgery presented to the emergency department with the symptoms of acute appendicitis and was admitted for surgery. No appendix was found in the surgical exploration. Cases presenting with the symptoms of acute appendicitis should have a detailed anamnesis taken with careful questioning, particularly related to previous surgery and a thorough physical examination should be performed. Before establishing the diagnosis of appendix agenesis, a comprehensive and careful exploration should be conducted after mobilizing the ileo-cecal region and ascending-colon. In addition, care should be taken to avoid injuring the ileo-cecal region, which is highly sensitive. Appendix agenesis should be kept in mind in cases presenting with the symptoms of acute appendicitis.