Development of the Decision Support System (DSS) used by the National Emergency Operations Centre in Switzerland began immediately after the accident at Chernobyl. The system will evaluate acceptable countermeasures following the accidental release of radioactivity in order to reduce ingestion dose. The DSS - not designed for the very early phase following the accidental release of radioactivity - contains four different modules: threat assessment, generation of countermeasures, specification and multi-criteria decision-making at a technical and political level. The project is now in a consolidation phase and the DSS is used mainly for generating exercise scenarios and for training the decision-makers. The Swiss DSS was developed with the help of all the responsible persons and organisations in Switzerland, especially the Army Staff who support the National Emergency Operations Centre in the event of an accidental release of radioactivity. Following intensive contacts with the various user groups during the development phase, suggestions and corrections have already been included at a very early stage of the project. An additional database for use by the Army Staff has been installed so that consequences with respect to the most important countermeasures and criteria can be generated automatically. One of the National Emergency Operations Centre's most important experiences with this kind of decision support was the need to integrate the system into its standard operating procedures. Integration is important not only for professional use, but also for the maintenance (new releases) and updating of databases. Without clearly defined responsibilities, such systems quickly lose their value and important knowledge and experience gets lost. Operational integration, maintenance and updating of databases are the main tasks which have to be guaranteed if a DSS is to be ready for use and effectively to support the decision-makers in crisis situations.