To investigate diagnostic aspects of invasive aspergillosis (IA) in allogeneic BMT recipients, the charts of 22 consecutive patients with IA transplanted in 1989-1995 were reviewed. IA was diagnosed 69-466 days (median 131 days) post BMT. In 16 patients (73%), a definite or probable diagnosis of IA was made during life. Respiratory symptoms were the presenting feature in half of the patients followed by neurological symptoms (27%). Chest X-ray revealed single or multiple nodular lesions in 10 patients; cavitation was observed in five patients. Tissue biopsy was the most common method of diagnosis (nine patients: lungs 6, liver 1, subcutaneous tissue 1, brain 1). Five IA cases were detected by nine guided fine needle lung biopsies in eight patients and without complications. Bronchoalveolar lavage was performed in 14 patients with findings suggestive of invasive pulmonary aspergillosis in eight cases. Lungs were the most common organ affected (90%) followed by central nervous system (41%). The diagnosis of IA is still difficult, and a large number of patients have advanced infection at diagnosis. Methods for early diagnosis are needed. Patients with a clinical suspicion of IA should be treated vigorously with antifungal agents during the diagnostic work-up.