Aspergillus fumigatus is frequently isolated from cystic fibrosis (CF) patients and is notorious for its role in the debilitating condition of allergic bronchopulmonary aspergillosis (ABPA). Although CF patients suffer from perpetual microorganism-related lung disease, it is unclear whether A. fumigatus colonization has a role in causing accelerated lung function decline and whether intervention is necessary. A. fumigatus morbidity appears to be related to cystic fibrosis transmembrane conductance regulator-dependant function of the innate immune system. A. fumigatus-colonized patients have a lower lung capacity, more frequent hospitalizations and more prominent radiological abnormalities than noncolonized patients. Treatment with antifungal agents can be of value but has several drawbacks and a direct effect on lung function is yet to be shown. A. fumigatus appears to have an important role in CF lung disease, not exclusive to the context of ABPA. However, a causal relationship still needs to be confirmed. Study observations and trends indicate a need to further elucidate the mechanisms of A. fumigatus interactions with the host innate immune system and its role in CF lung morbidity.