Defining bronchiectasis aetiologies: this patient had a diagnosis of chronic obstructive pulmonary disease based on smoking history and airflow limitation. The computed tomography scan indeed shows apical emphysema. However, this scan also shows bronchiectasis and a dilated trachea suggesting Mounier–Kuhn syndrome as an aetiology for the bronchiectasis. Reviewing the history carefully showed recurrent childhood infections further supporting this as an aetiology. As bronchiectasis-COPD overlap syndrome has a poorer outcome, defining the aetiology of bronchiectasis is important.