Intestinal malrotation is a rare anomaly of rotation and fixation of the midgut. Left-sided appendicitis occurs in association with two types of congenital anomalies, situs inversus and intestinal malrotation. We describe a rare case of left-sided acute appendicitis with intestinal malrotation in a 14-year-old boy, in which computed tomography (CT) was useful for a preoperative diagnosis.