The incidence of haemorrhagic complications of intracranial pressure monitoring (ICPM) has previously been reported. However, in these studies, the techniques employed to access the inside of the cranium varied. While 3-mm essentially blind 'twistdrill' craniostomies have been used, their role has been limited for fear of haemorrhagic sequelae. This has also restricted their use in clinical applications other than ICPM. We conducted a prospective observational study looking at haemorrhagic complications of the twistdrill in order to determine its safety and whether it has a role in other clinical settings. Over the period January 1994-February 2001, 941 patients had 1032 twistdrill procedures. There were 550 (58.4%) male patients and 391 (41.6%) female. The age range was 3 months to 93 years (median age 35 years). Only four procedures (0.38%) caused clinically significant bleeds attributable to the twistdrill --all of which were managed conservatively without requiring surgical evacuation. We conclude that twistdrill craniostomies are safe and that their use could be extended to other neurosurgical procedures and potentially to ICPM in non-neurosurgical centres.