We present a case of 39 year old woman who developed malignant external otitis (m.e.o.) of Pseudomonas aeruginosa aetiology during pancytopenia after autologous bone marrow transplantation (ABMT). The infection was probably of endogenous origin. 7 days before ABMT otolarygological examination including otoscopy and external ear lavage was performed. Slight inflammatory reaction of external ear was accompanied by the massive involvement of middle ear followed by infiltration of petrous pyramid and mastoid process and finally facial and vestibulocochlear nerve paralysis. Initially the symptoms indicated subarachnoid haemorrhage. Mononuclear cells detected in cerebrospinal fluid as well as CT scan were suggestive of leukaemic infiltration. The latter was negated by immunophenotyping of cerebrospinal fluid cells and MR imaging. Antibiotic therapy resulted in clinical improvement. Life-threatening complications are not frequent after ABMT (transplant related mortality--14/310 (4.5%) in our center). We have met m.e.o. for the first time. At present--13 months after ABMT the patient shows slight symptoms of nerve VII and VIII paresis and remains in complete remission of acute leukaemia. We emphasize the importance of proper preparation of patients for high dose chemotherapy followed by bone marrow transplantation as well as diagnostic difficulties related to pancytopenia.