A more closed farming system will enhance the success of disease eradication programmes, because the introduction or re-introduction of infectious diseases is less likely. The objective of the study was to obtain input for the development of an on-farm decision support model to calculate the economic consequences of a more closed farming system. The input was based on bovine herpesvirus 1 (BHV1), since there were numerous data on this disease, but a more closed farming system will prevent introduction of other diseases as well (i.e. bovine virus diarrhoea virus (BVDV), L. hardjo, and S. dublin). Direct animal contacts, such as purchase of cattle, participation in cattle shows, and cattle that escape and mingle with other cattle, were found to be important risk factors for the introduction of BHV1. Furthermore, the use of protective farm clothing was found to be an important preventive factor. The effect of an IBR outbreak at an IBR-free farm on milk production caused limited losses of on average 0.9 kg per cow per day during 9 weeks, but the variability was high (95% CI 0-2 kg). Nine percent of Dutch IBR-free dairy farms that were also at risk for BVDV, L. hardjo or S. dublin had one introduction per year of one of these four diseases. All these results were incorporated in the economic model. Management measures to reduce the probability of introduction of BHV1, the costs of these measures, and the risk reduction after these measures were obtained from other sources. The calculations showed that the implementation of a more closed system will be profitable for most farms. The profitability will increase when a farm is at risk for more diseases, but will decrease when farms are limited in their facilities to rear replacement heifers or when a large proportion of pasture adjoins pasture of other cattle farms.