Mucinous cystadenoma of the appendix is an unusual neoplasm, which represents one of the histological subtypes of mucocele. Giant appendiceal cystadenomas are extremely rare and most commonly presented with palpable abdominal mass, chronic right lower quadrant (RLQ) pain, or could be asymptomatic. We present a 51-year-old female with clinical picture of acute appendicitis and a giant mucinous cystadenoma of the appendix with low grade dysplasia.