A postal survey of adverse events associated with bone marrow biopsy (aspiration biopsy with or without trephine biopsy) was carried out among British Society of Haematology members, between 1995 and 2001. A total of 26 adverse events, including one death directly attributable to the procedure, were reported among an estimated 54 890 biopsies. The most frequent and most serious adverse event was haemorrhage, reported in 14 patients, necessitating blood transfusion in six patients and leading to the single death. The potential risk factors most often associated with haemorrhage were a diagnosis of a myeloproliferative disorder, aspirin therapy or both. Other potential risk factors were warfarin therapy, disseminated intravascular coagulation and obesity.