Anatomical studies and reports on the sternalis muscle are continuously being conducted, which is clinically important for mastectomy and breast augmentation. This report relates to the bilateral sternalis muscle observed in the cadaver of a 90-year-old Korean man during educational cadaveric dissection in the department of anatomy. The right sternalis muscle originates from the 5th to 7th rib cartilages and forms an aponeurosis at the lateral edge of the body of the sternum. It crosses the midline of the body of the sternum, becomes a belly again and inserts into the pectoralis major muscle at the height of the 1st and 2nd intercostal spaces on the left. There are two sternalis muscle on the left side. The first left sternalis muscle originates from the 6th to 7th rib cartilages, forms an aponeurosis at the height of the 4th rib cartilage and inserts into the midline at the height of the sternal angle. The second left sternalis muscle originates from the 5th intercostal space, forms an aponeurosis at the height of the 3rd rib cartilage and inserts into the lateral edge of the body of the sternum. This case report intends to examine the statistics of sternalis muscle found in Korea, along with studies on the variation, and to clarify the anatomical and clinical significance of th...