Tracheal collapse in dogs is a condition characterized by incomplete formation or weakening of the cartilaginous rings of the trachea resulting in flattening of the trachea. It can be congenital or acquired, and extrathoracic or intrathoracic. Tracheal collapse is a dynamic condition. Collapse of the cervical trachea or extrathoracic occurs during inspiration; collapse of the thoracic trachea or intrathoracic occurs during expiration. Tracheal collapse is most commonly found in small dog breeds, including the Chihuahua, Pomeranian, Toy Poodle, Shih Tzu, Lhasa Apso, Maltese, Pug, and Yorkshire Terrier.