Aspergillus is a genus of fungi commonly found in all environments. Remarkably, only a few species cause disease and equally remarkably, those same species cause multiple diseases. In the lung, exposure to the fungus, the immunological status of the individual and the condition of the lung determine the pattern of disease. In asthmatic patients and those with cystic fibrosis, allergic bronchopulmonary aspergillosis (ABPA) is a complication that reduces pulmonary function and, in asthmatics, is substantially improved by itraconazole therapy. Patients with pre-existing lung cavities develop aspergillomas (fungal masses inside the cavity). Aspergillomas carry a 40% 5 years survival, and it not clear whether antifungal therapy is helpful. Similar in presentation to aspergilloma is chronic necrotizing pulmonary aspergillosis (CNPA). Development of new or expansion of existing pulmonary cavities with surrounding paracavitary shadowing is the hallmark of CNPA These two entities are probably a continuum of the same pathological process. Patients with CNPA respond to systemic antifungal therapy, but this may need to be lifelong. Surgery is appropriate for isolated aspergillomas, but not pleural or multicavity lesions. Aspergillus empyema is a complication of aspergilloma and CNPA, or surgery for these diseases and is slow to respond to treatment.