Since its discovery as an agent of mycetoma nearly a century ago, Pseudallescheria boydii with its asexual (synanamorphic) form, Scedosporium apiospermum, is now recognized as an important emerging opportunistic pathogen causing invasive mycosis in immunocompromised patients. The clinical spectrum of pseudallescheriasis is wide. Invasive disease of the lung, CNS and dissemination are serious manifestations in immunocompromised patients. This organism responds poorly to amphotericin B, and its histopathologic resemblance to aspergillosis often results in a delay in diagnosis. In vitro data, animal models and accumulating clinical experience support the use of voriconazole as a primary treatment for pseudallescheriasis. This paper reviews the microbiology, ecology, epidemiologic trends, clinical manifestations and current treatment options of pseudallescheriasis.