Crude delivery rate is used to calculate requirements for consultant anaesthetic sessions in the UK, but this calculation is arbitrary and ignores differences in case-mix between units. The term 'epidural rate' is commonly used to indicate regional anaesthetic activity but has never been defined. We challenge both these concepts and illustrate our argument by applying different definitions of obstetric anaesthetic activity to prospectively collected maternity data from 31 211 deliveries over 5 years in two hospitals. Number of anaesthetic interventions is a more accurate reflection of obstetric anaesthetic activity than number of deliveries, with Northwick Park Hospital having about 200-600 more deliveries per year than Chelsea & Westminster Hospital but about 300-400 fewer anaesthetic interventions per year. 'Epidural rate' varied by up to 30% according to the definition used. We conclude that number of anaesthetic interventions should replace crude number of deliveries as a measure of obstetric anaesthetic activity, and that the term 'regional anaesthesia rate' should replace 'epidural rate'.