Invasive fungal disease of humans caused by species of the genus Aspergillus Micheli ex Linnaeus has become a significant and prevalent problem in contemporary medicine, particularly with regard to the compromised host. This review addresses the current status of invasive aspergillosis, including microbiological, clinical, and pathologic aspects. Diagnostic and therapeutic considerations are discussed with a view toward early and aggressive intervention in order to prevent the high mortality rate associated with aspergillosis.