The inadvertent 'plunging' of an instrument into the cranial cavity is a feared complication of drilling a burr hole and while anecdotes abound, little is known about the extent or the consequences of this problem. A survey by anonymous postal questionnaire of 304 neurosurgeons in Britain and Ireland was conducted to analyse the extent of this complication. Of respondents, 65.6% had experienced 'plunging', 22.3% having 'plunged' at least twice, indicating a high prevalence of this complication. The Cushing perforator was implicated by most. 'Plunging' carried a 12% risk of death or permanent neurological morbidity. The authors analyse the prevalence and significance of this preventable complication, and discuss various options available to minimize its occurrence.