Wereport a female patient with left atrial wall invasion from pulmonary aspergillosis. She had been treated for diabetes mellitus. Pulmonary aspergillosis extended to the left atrial wall via the left pulmonary vein and formed a polypoid lesion in the left atrium. The polypoid lesion was composed of thrombus, and the thrombus increased in size to become large, and it showed invagination into the mitral valve during diastole. Weconsidered that the thrombus was formed on the injured endocardium. Severe invasive aspergillosis thus could occur in a mild systemic immunocompromisedhost. (Internal Medicine 40: 250-254, 2001)