Over the past two decades, the incidence of invasive aspergillosis (IA) has risen inexorably. This is almost certainly the consequence of the more widespread use of aggressive cancer chemotherapy regimens, the expansion of organ transplant programmes and the advent of the acquired immunodeficiency syndrome (AIDS) epidemic. Despite the development of new approaches to therapy, IA still remains a life-threatening infection in immunocompromised patients and is the most important cause of fungal death in cancer patients. It is clear that the prevention of severe fungal infection by the use of effective infection control measure should be the priority of the teams involved in managing at-risk patients. The evidence from clinical and molecular epidemiological studies is reviewed and current thinking on sources and routes of transmission of the organism are discussed. Our increasing understanding of these has led to the development of a variety of environmental and general strategies for the prevention of IA. It is anticipated that these, coupled with the use of prophylactic antifungal agents active against Aspergillus spp., will have a significant impact upon the morbidity and mortality associated with this infection.