Allergic bronchopulmonary aspergillosis (ABPA) is an uncommon condition which may complicate asthma and cystic fibrosis; it is seldom considered life-threatening. We report a well 8-year-old boy with cystic fibrosis and normal lung function who progressed to respiratory failure over several days, attributable to ABPA. He recovered with non-invasive ventilation and oral corticosteroid and antifungal medications, regaining normal lung function within 2 months. To our knowledge, such an acute severe presentation of ABPA in a previously well child has not been reported before.