In a retrospective study of over 1,500 patients who underwent bone marrow transplantation between 1980 and 1987, the incidence of invasive candidal or mold infection was 11% and 4.5%, respectively. Candidemia alone occurred in 46, candidemia and tissue infection in 56, and tissue infection alone in 69 of 1,510 patients analyzed. Aspergillus infection alone occurred in 69, other mold infections occurred in four, and Aspergillus plus other mold infections in two of 1,658 patients analyzed. Median time to onset of candidal infection was 2 weeks and of mold infections 6 weeks after transplantation. Overall mortality for patients with candidal infection was 73% and for those with Aspergillus or other mold infections, 84%. Death occurred in 39% of patients with candidemia alone, 90% of patients with candidal tissue infection with or without candidemia, and 100% of those with mixed infection. The death rate was 75% for patients infected with Aspergillus alone, 83% for those infected with other molds with or without Aspergillus, and 100% when there was coinfection with Candida or cytomegalovirus. The probability of occurrence of Aspergillus infection was influenced by patient age, donor match, type of conditioning regimen, and occurrence of acute graft-versus-host disease (GVHD), while the occurrence of candidal infection was influenced by additional factors including underlying disease and GVHD prophylactic regimen. In contrast to some published reports, the risk of Aspergillus infection was not significantly altered by infection prevention methods, including provision of a protective environment. These data confirm both the high incidence and severity of fungal infection after bone marrow transplantation and underscore the urgent need for more effective prophylaxis and treatment.