Acute appendicitis is one of the most common clinical presentations among the patients with acute abdominal pain. However, a through clinical and surgical evaluation is essential to manage atypical conditions such as carcinoids and the tumors of appendix or mucocele appendix. Here, we present a case with mucocele of appendix vermiformis due to mucinous cystadenoma with carcinoma in situ component. This case indicates that atypical presentations and clinical findings should be carefully managed in the patients with suspicious acute appendicitis in surgery. This is especially essential in the patients with appendiceal mass or mucocele in order to minimize complications.