Tracheobronchomalacia (TBM) is a rare condition that occurs when the walls of the airway (specifically the trachea and bronchi) are weak. This can cause the airway to become narrow or collapse. There are two forms of TBM. One typically develops during infancy or early childhood (primary TBM). The other is an acquired form usually seen in adults (acquired or secondary TBM). Some people with TBM may initially have no signs or symptoms. Most cases of primary TBM are caused by genetic conditions that weaken the walls of the airway, while the acquired form may occur due to trauma, chronic inflammation, and/or prolonged compression of the airways. The acquired form is often seen in adults with common respiratory conditions such as asthma, chronic bronchitis, and emphysema. In many cases, the cause is not known.