Aspergillus is a ubiquitous soil-dwelling mould found in organic debris, compost, dust, rotted plants and food. There are approximately 200 species of aspergillus, some of which are pathogenic and cause aspergillosis (an infection, a growth, or an allergic response due to the aspergillus fungus). The aspergillus fungus grows best at 37 C and infection is acquired primarily through the inhalation of airborne spores entering the respiratory tract where the mould colonises to other sites (Soubani and Chandrasekar 2002; Linc et al 2001). Environmental factors such as water supply, inadequate filtration of outside air, and vacuum cleaning in hospital settings have been identified as risk factors for developing aspergillosis (Donnelly 2000; De La Rosa et al 2002). Bone marrow transplant (BMT) patients are by necessity immunocompromised, rendering them highly vulnerable to opportunistic infections. Aspergillosis is a common, life threatening complication of BMT, particularly in patients receiving grafts from unrelated donors, so called allogeneic transplants (Williamson et al 1999). Wingard (1999) suggests that with the availability of effective prophylaxis of bacterial and viral infections, invasive fungal infections have therefore become the major cause of infectious morbidity and mortality in patients undergoing BMT. Following BMT, the immune system recovers in a set pattern: cytolytic cells such as natural killer cells are first to recover followed by B-cell and then T-cell function. The time at which opportunistic infection by bacterial, viral, fungal and protozoal organisms occur can vary at different periods post transplant (Fox et al 2003; Wright-Kanuth and Smith 2001). Aspergillus can usually cause infection from day 20 to day 30 when the patient remains profoundly neutropenic post BMT (Patterson 1999; Wingard 1999; Maertens et al 2001). Fungal infections often follow bacterial infections if neutropenia continues (Linc et al 2001), and must be suspected if fever persists despite the usage of broad-spectrum antibiotic treatment (D’Antonio et al 1996). The diagnosis of systemic fungal infection in BMT patients is not straightforward due to the risks A bs tr ac t Many complications can occur following a bone marrow transplantation including that of opportunistic fungal infections such as aspergillus. This article discusses the care of a patient who was diagnosed with acute lymphoblastic leukaemia and subsequently received an allogeneic bone marrow transplant. A description of aspergillus infection and the interventions used to prevent and manage this complication are explored. Finally, the effectiveness of the care delivered is discussed along with the implications for future nursing practice.