A twenty-five days old girl, admitted to pediatric pulmonology clinic, with collapse on the anterior chest wall while breathing. Physical examination revealed total retraction of the chest wall especially on the upper part, paradoxical chest wall movements with respiration, and a raphe extending from the umbilicus to the lower end of the sternum. Hypoplasia of the inferior and non-development of the superior segment of the sternum was shown on 3-dimensional(3D) thorax CT. At the age of fifty-six days, she had been operated. Due to the large defect, primary closure couldn’t be performed and the sternum was reconstructed with the cartilage obtained from the tissue around the ribs. The sternal cleft is a rare malformation; complete assessment, based primarily on thoracic imaging is required for diagnosis. Also cardiac, abdominal and cranial imaging for concominant malformations should be performed; our patient had none. Immediate surgical management is essential to avoid possible complications.