THIS paper is a retrospective study of thirty-nine patients with lung disease, caused by aspergillus fumigatus, seen in two large general hospitals over a ten year period. The study was undertaken to establish the pattern and distribution of pulmonary aspergillosis in this group with particular emphasis on the nature of the underlying disorder, management and outcome. The patients fell into three well-defined categories: 1. Localized aspergilloma (fungus ball, mycetoma)-20 patients. 2. Allergic bronchopulmonary aspergillosis (ABPA)-12 patients. 3. Invasive aspergillosis — 7 patients. The aspergilloma group was characterized by severe, preexisting lung disease, poor pulmonary function and, in 50% of cases, life-threatening heamoptysis. This complication was treated surgically (5 cases), by embolisation of the bronchial artery (3 cases) or conservatively (2 cases) depending on clinical and physiologic status. In the ABPA group, all patients had asthma. Seven patients (58%) had bronchographically proven bronchiectasis at the time of diagnosis of ABPA and all but one required long-term oral steroid therapy. The 7 cases of invasive aspergillosis comprised 5 patients with underlying neoplasm, one with myelofibrosis and one with systemic lupus erythematosis most of whom were on some form of immunosuppressive therapy. Surprisingly, clinical and radiologic findings were subtle. In 4 of these 7 cases (57%), aspergillosis precipitated the terminal event and in five of these cases (71%), the diagnosis was not made until post-mortem examination. These data emphasise the diverse mechanisms by which aspergillus fumigatus can cause serious pulmonary pathology. Despite the wide differences in etiopathogenic mechanisms of the three groups, a striking common denominator in this group was the advanced stage of the disease at the time of diagnosis. There is a need for heightened awareness of the importance of aspergillus fumigatus as a complication of fibrotic lung disease, of ABPA in asthma and of invasive aspergillosis in neoplasm and disease associated with immunosuppression.