Pulmonary aspergillosis is a serious threat to those immunocompromised as a result of disease or therapy, and has been identified as a major cause of morbidity and mortality in asthmatic and cystic fibrosis patients. Pulmonary aspergillosis can occur in three principal forms: saprophytic, allergic and invasive. Saprophytic aspergillosis involves colonisation of the airways, without invasion or damage of viable tissue, and may present as an aspergilloma (fungus ball) consisting of a tangled mass of mycelium, fibrin, inflammatory cells and epithelial-cell debris. Necrotic tissue also may be invaded but usually only in those severely immunocompromised. Allergic aspergillosis is referred to frequently as allergic bronchopulmonary aspergillosis (ABPA), and may occur in approximately 25% of asthmatic and 10% of cystic fibrosis patients. ABPA presents as a non-infectious, potentially fatal inflammatory disease where antigens released by the fungal mycelium provoke an immune response. Invasive aspergillosis is probably the most serious form of the disease and involves the invasion of viable tissue. It occurs predominantly in patients with pre-existing lung damage, and can spread to other organs and distant sites in the body. Aspergillomas may be detected on chest X-ray as spherical-shaped objects, whilst allergic aspergillosis may be visualised by radiological techniques and computed tomography (CT) scan. Surgery may be employed in the case of aspergilloma, and chemotherapy relies upon the use of amphotericin B (liposomal and aerosolised) and itraconazole.