In order to clarify the present state of opportunistic fungal infections increasing in incidence in autopsy cases, all autopsy cases from 1966 to 1975 reported in the Annual of Pathological Autopsy Cases in Japan were reviewed. Of the total 233,130 autopsy cases, mycoses were present in 4,340 (1.86%). The incidence of mycoses has strikingly increased during the recent five-year period. In Japan, the mycoses most frequently occurring in autopsy cases were candidiasis (32.28%), aspergillosis (23.08%), cryptococcosis (9.63%), and mucormycosis (2.90%). These occurred more frequently in younger persons and were most commonly secondary and deep-seated infections (95.78%). Among the primary diseases associated with mycoses, aplastic anemia (14.36%), leukemia (9.89%), malignant lymphoma (5.73%), multiple myeloma (4.68%), and systemic lupus erythematosus (4.62%) were most frequent. The incidence of the primary diseases associated with mycoses is increasing extraordinarily, and this seems to be strongly related to the modern therapy of using high doses of anticancer or immunosuppressive agents.