Syndromic surveillance systems are commonly presented in the literature but few are rigorously evaluated. We present and test an evaluation framework to examine which events can and cannot be detected, the time to detection and the efficacy of different syndromic surveillance data streams. This was achieved using four national syndromic surveillance systems in England and simulating a number of possible disease events (e.g. outbreak of pandemic influenza, (Cryptosporidium) outbreak and deliberate anthrax release). This methodology can be widely adopted to provide more empirical analysis of the effectiveness of syndromic surveillance systems worldwide.