BACKGROUND: Multifaceted interventions improve the quality of preventive cardiovascular care in general practice when applied in small-scale research trials. AIM: To test the transferability of observations from research trials on preventive cardiovascular care to a real-world situation and, therefore, evaluate the effectiveness of a nationwide project with a large number of practices. The intervention comprised a combination of conferences, dissemination of manuals, and support from trained non-physicians during outreach visits. DESIGN OF STUDY: A controlled before-and-after trial with two arms: multifaceted support versus no special attention. Analysis after 2 years. SETTING: 617 general practices in The Netherlands. METHOD: Outcomes measures were the compliance rates for 15 indicators. Structure-of-care indicators included the use of reminders, specific computer files, written protocols, and special clinics. Process-of-care indicators included the assessment of modifiable risk factors and use of a minimal contact intervention (MCI) for smoking cessation. Compliance of general practitioners (GPs) was assessed using self-administered questionnaires. RESULTS: The intervention group improved on all eight of the structure-of-care indicators when compared to the control group. A positive effect was also found on the extent to which the GPs measured blood pressure in 60-year-old patients and on the use of an MCI for smoking cessation. No effect was found on the completeness of the risk-factor profiles that the GPs assessed in specific groups of high-risk patients. CONCLUSION: The nationwide intervention appeared to improve certain aspects of preventive cardiovascular care. Nevertheless, the National Association of GPs decided to stop the project. This decision was made within the context of discussions about the heavy workloads and insufficient incomes being experienced by GPs.