Posaconazole is a second-generation triazole antifungal agent with a broad spectrum of activity that includes Aspergillus spp., Candida spp. and the Zygomycetes. In the US, posaconazole oral suspension administered three times daily is indicated for prophylaxis against invasive Aspergillus and Candida infections in patients aged > or =13 years who are at high risk of developing these infections because of immunosuppression, such as haematopoietic stem cell transplant (HSCT) recipients with graft-versus-host disease (GVHD), or those with haematological malignancies with prolonged neutropenia as a result of chemotherapy. EU-approved prophylactic indications for posaconazole are similar to those in the US. Posaconazole provided effective prophylaxis against invasive fungal infections and was generally well tolerated in two large, well designed trials in HSCT recipients with GVHD, or patients receiving induction-remission chemotherapy for acute myeloid leukaemia (AML) or myelodysplastic syndrome (MDS) that was expected to result in prolonged neutropenia. It offers coverage of clinically relevant pathogens and is potentially associated with fewer drug-drug interactions than other licensed triazole antifungal agents. Its usefulness in some patients may be limited by the lack of an intravenous formulation, although one is currently being developed. As with other antifungal agents, concerns remain regarding the potential emergence of resistance to broad-spectrum antifungal prophylaxis with posaconazole. Despite this, posaconazole is a valuable emerging option for use as prophylaxis against invasive fungal infections in immunocompromized patients who are at high risk of developing these infections.