Within the framework of the project 'Obstetric Peer Review' (Verloskundige Onderlinge Kwaliteitsspiegeling, VOKS) differences between Dutch hospitals concerning various obstetrical interventions were investigated. Using data of the Perinatal Database of the Netherlands from hospitals with at least 2000 newborns in the 5-year period 1987-1991, remarkable differences in frequencies of labour induction, caesarean section and vaginal operative deliveries can be shown, even when these interventions were considered within homogeneous subgroups with respect to pregnancy- or delivery-related complications. The incidence of caesarean section (and labour induction and vaginal operative delivery) appeared to depend more on the specific hospital policy than might be explained by populations differences alone. These intervention differences between hospitals clearly demonstrated the need to carry out a multivariate analysis to compare hospitals in a relevant and unbiased way, while adjusting for these population differences. This will estimate the intervention risks in a way which allows a fair comparison of hospital intervention policies.