The aim of this study was to present the diagnostic problems in pts treated for invasive aspergillosis (IA) in the IIIrd Clinic of the Institute of Tuberculosis in the years 1993-2005. The material consisted of clinical documentation of 18 pts. 15 out of 18 pts (83,4%) died. In all those cases autopsy examination was done. In 13 pts IA was the main and in another 2 only the accessory cause of death. All pts were treated with corticosteroids and/or cytostatic drugs because of lung cancer (13 pts), haematologic disorders (1 pts), Wegener's granulomatosis (3 pts) and idiopathic pulmonary fibrosis (1 pts). In 13 out of 18 pts granulocytopenia was revealed (on an average from 0,008 x 10(9)/L to 0,95 x 10(9)/L) one month before death. In 13 pts IA was limited to the lungs, in 5 others there were also fungal lesions in brain, kidneys, liver, spleen, pleura, pericardium and heart. Pts with disseminated form of IA had significantly lower granulocyte count and were treated with higher doses of corticosteroids than others. Immunosupressive drugs and granulocytopenia can be regarded as predisposing factors. IA was diagnosed before death only in 5 out of 18 pts. This was mainly caused by the lack of the symptoms of infection (4 pts) and negative results of mycological (6 pts) and serological examination (8 pts). We should underline that mycological examination was only done in 11 pts and serological examination of blood for fungal antigen only in 6 pts. We conclude that mycological infection ought to be searched in all pts treated with high doses of corticosteroids and those with prolonged granulocytopenia, especially if they have the symptoms of infection which does not respond to antibiotic therapy.