Aspergillus produces diverse pulmonary manifestations, its clinical spectrum extending from harmless saprophytic colonization to universally lethal disseminated infection. Management of the conditions produced by Aspergillus is also diverse and may consist of either observation or treatment with corticosteroid agents or amphotericin B. The factors that influence the expression of Aspergillus into a specific clinical entity are not well understood, but are believed to be related to immune status, both pulmonary and systemic, and the genetic composition of the host.