A new assessment methodology is presented for the benefits of flood warning that applies both tangible and intangible benefits from warning generation and dissemination using a multi-criteria analysis (MCA). The resulting decision support tool allows benefits to be scored transparently, reinforced by Geographical Information System (GIS) procedures. A wide range of benefits are scored including: protection of key infrastructure, avoided social impacts, timely operation of flood defences and avoided risks to life from the flood hazard. Pilot testing on some 22 sites at a variety of scales (catchments and flood warning areas) showed that the method works effectively when making 'like for like' comparisons, considering a wholly new system for large catchments, or upgrades to warning and dissemination systems in sub-catchment flood warning areas. The methodology promotes consultation and data interchange between the warning organisation and end-users in order to prioritise particular areas of need for new or improved systems.