Allergic bronchopulmonary aspergillosis (ABPA) is a disease affecting patients with asthma as well as those with cystic fibrosis. The clinical picture of ABPA is characterized by symptoms of wheezing, pulmonary infiltrates, bronchiectasis, and in later stages, pulmonary fibrosis. Since patients with cystic fibrosis may have several of these clinical features as part of their disease process, it is important to distinguish the overlap of this entity so that therapy may be instituted in a timely manner. This paper will discuss the clinical diagnosis, immuno-pathology and treatment of ABPA as it affects patients with cystic fibrosis.