Reports have focused on the emergence of moulds as pathogens in recipients of hematopoietic stem cell transplants. To review the incidence of and risks for mould infections, we examined the records of 5589 patients who underwent hematopoietic stem cell transplantation at the Fred Hutchinson Cancer Research Center (Seattle) from 1985 through 1999. After 1992, the incidence of invasive aspergillosis increased in allograft recipients and remained high through the 1990s. Infections with non-fumigatus Aspergillus species, Fusarium species, and Zygomycetes increased during the late 1990s, especially in patients who received multiple transplants. Although infection caused by Scedosporium species was common in patients who had neutropenia, infection caused by Zygomycetes typically occurred later after transplantation, when patients had graft-versus-host disease. The overall 1-year survival rate was equally poor (similar20%) for all patients with mould infections. The results of the present study demonstrate the changing epidemiology of mould infections, emphasizing the increasing importance of amphotericin B--resistant organisms and the differences in risks and outcome of infection with different filamentous fungi.