A survey of morbidity and mortality of bone marrow aspiration and trephine biopsy was carried out for the British Society of Haematology, covering the 12 months of 2002. Fifty-three centres reported 13,506 procedures, comprising 3927 aspiration biopsies and 9579 combined procedures. There were 17 adverse events including nine instances of haemorrhage, four infections and one haemorrhage complicated by infection. Two trephine biopsy needles broke during the procedure. One patient suffered considerable pain for 2 weeks. The adverse event may have contributed to death in two patients and in a third patient was life-threatening. Risk factors for adverse events were identified.