Intracranial haemorrhage (ICH) is a known grave complication of leukaemia and has been described post mortem following bone marrow transplantation (BMT). Ante mortem following BMT, the incidence and significance of ICH is not well defined. The records of 471 bone marrow transplantation recipients over 11 years at the Hadassah University Hospital Bone Marrow Transplantation Department were reviewed. The relevant data of all patients with ICH were analysed. A resolute diagnostic and treatment protocol for subdural haematomas had been employed. The indication for transplantation in 273 of the patients was leukaemia. Thirteen of these patients developed subdural haematomas within 42 days of the transplant, and nine of these haematomas were bilateral. None of the 198 patients with other malignancies or nonmalignant indications for BMT (predominantly aplastic anaemia and beta thalassaemia major) had subdural haematomas. One thalassaemia patient and three leukaemia patients had intracerebral haematomas. There was no mortality or major morbidity from the subdural haematomas, which were all successfully resolved. In contrast, all of the patients with intracerebral haematomas consequently died. Subdural haematomas occur in approximately 5% of patients with leukaemia following BMT, but the clinical outcome is relatively benign. Intracerebral haematomas are a sporadic, lethal complication following BMT.(ABSTRACT TRUNCATED AT 250 WORDS)