Within the framework of the 'Obstetric Peer Review' project (Verloskundige Onderlinge Kwaliteitsspiegeling, VOKS) statistical models have been developed to predict department specific intervention rates, based on the distribution of risk factors in each department. Subsequently the difference between the expected number of interventions (labour inductions, caesarean sections and vaginal operative deliveries) and the actual numbers were calculated for each year and subpopulation defined by the level of prematurity. Data used were available from the Perinatal Database of the Netherlands (Landelijke Verloskunde Registratie, LVR) concerning the years 1988-1992. Even after adjusting for many clinical risk factors the interdepartmental differences of intervention rates are both clinically relevant and statistically significant. It was also obvious, especially for the term population, that departments showed a consistent pattern with respect to the difference between their expected and observed intervention rates over these 5 years.