Appendectomy is the most common non-obstetric surgical intervention in pregnant patients. In rare cases, deciduosis can develop during pregnancy in the appendix and cause inflammation through appendiceal occlusion by ectopic decidua tissue. We report a 28-year-old woman at 32 weeks of pregnancy, who presented at the emergency room with the diagnosis of an acute appendicitis. After successful appendectomy and histopathological examination of the appendectomy specimen, a diagnosis of appendiceal deciduosis with acute appendicitis was established. Here, we discuss the origin of appendiceal deciduosis, as well as its clinical and histopathological presentation.