Systemic mastocytosis is characterized by abnormal growth and accumulation of mast cells in various organs. Gastrointestinal (GI) symptoms are common disease manifestations in this disease and can significantly impair the quality of life. Signs of GI systemic mastocytosis include steatorrhea, malabsorption, hepatomegaly, splenomegaly, portal hypertension, and ascites. Acute appendicitis as a presenting feature in systemic mastocytosis has not been reported in the literature previously. In this report, we discuss the case of a female patient with systemic mastocytosis (c-KIT D816V (+)) who was admitted for right-sided acute abdominal pain. Laboratory study revealed an normal white blood cell count with eosinophilia and an elevated serum tryptase level of 23 μg/l. CT of the abdomen and pelvis showed an enlarged appendix of 12 mm in diameter, with minimal wall enhancement. Laparoscopic appendectomy was performed. The appendix was found to be hyperemic and firm, and it was densely adherent to the posterior cecum, the surrounding peritoneal wall, and the overlying mesenteric fat. Pathology revealed acute appendicitis with greater than 30 mast cells per high-power field by immunoperoxidase studies with mast cell tryptase and CD117. The patient subsequently improved and was discharged home. This case is the first reported case with a histological diagnosis of acute appendicitis resulting from mast cell infiltration. Physicians should be aware of acute appendicitis as a manifestation of systemic mastocytosis. Prompt diagnosis and management may prevent potentially fatal complications of appendiceal perforation and peritonitis.