Decidualization of endometrial tissue is a physiologic phenomenon during pregnancy caused by high progesterone levels. Decidual cell groups outside the endometrium are named ectopic decidua and this condition has first been described by Walker in 1887. Ectopic decidua of the appendix (EDA) is a rare entity that can present with abdominal symptoms mimicking appendicitis. The treatment of EDA is surgical and the evolution is favorable in the majority of cases. Definitive diagnosis is performed by histopathological analysis.