Invasive mould infection, e. g. aspergillosis in the first place, is a common infection in immunocompromised patients. The diagnosis of invasive mould infection is difficult in the absence of confirmation by tissue biopsy and histological studies. Therefore, prevalence of invasive mould infections at the School of Medicine of the Leipzig University between 1992 and 1994 was investigated. The diagnosis of invasive mould infection was suspected on clinical, mycological, and radiological findings. The definitive diagnosis was obtained by identification of characteristic mould hyphae on stained smears, and/or positive culture, and/or the detection of Aspergillus antigen (Pastorex) in serum, bronchial secretion, or bronchoalveolar fluid, and confirmed by histopathology. In altogether 21 patients the definitive diagnosis invasive mould infection was recorded, among them 20 invasive aspergilloses. Underlying diseases were leukaemia (n = 11), aplastic anaemia (n = 2), non-Hodgkin-lymphoma (n = 1), systemic lupus erythematosus (n = 1), kidney transplantation (n = 1), peritonitis after Billroth II anastomosis (n = 1), Polymyalgia rheumatica (n = 1), AIDS plus Burkitt lymphoma (n = 1), glioblastoma (n = 1), and subarachnoid haemorrhage (n = 1). As causative fungi were isolated: Aspergillus fumigatus (n = 13), Aspergillus terreus (n = 1), Aspergillus flavus as rare simultaneous injection with the basidiomycete Coprinus spec. in a leukaemic patient (n = 1), and the dematiaceous fungus Scedosporium prolificans in an AIDS patient with Burkitt lymphoma (n = 1). In four patients the invasive mould infection was confirmed histopathologically without isolation and differentiation of the causative agent. Nineteen of the 21 patients with invasive mould infections died corresponding to a mortality rate of 90%.