Congenital laryngeal stridor is a defect that is present at birth. During fetal development, the structures in the larynx may not fully develop. As a result, there is a weakness in these structures at birth, causing them to collapse during breathing. In children, congenital laryngeal stridor is the most common cause of chronic stridor. 60% of infants born with congenital laryngeal stridor will have symptoms in the first week of life. Most other infants will show symptoms by 5 weeks old.