The incidence of invasive nosocomial aspergillosis was studied in leukemia patients at an oncology center from 1964 to 1983. A total of 97 cases of aspergillosis occurred in 1,866 patients, yielding an overall case rate of 5.2 cases per 100 patients and an incidence rate of 9.1 per 10,000 patient days. The highest incidence rate was in patients with chronic myelogenous leukemia (13.7 cases per 10,000 patient days), followed by patients with acute myelogeneous leukemia (10.6 cases per 10,000 patient days). Subdividing patients after 1978 into those receiving bone marrow transplantation and those who did not demonstrated the predisposition of transplant recipients to aspergillosis. The rates of aspergillosis among those patients who did not receive a bone marrow transplant were highest for patients with acute myelogeneous leukemia. Increases in the annual rates of aspergillosis over time coincided with the level of internal renovation activity and major construction projects upwind of patient care facilities.