A method for plant pest risk assessment using historical incursion data is currently being developed by CSIRO and PBCRC to identify and prioritise high impact plant pests and diseases. By analysing the biological and pathway data for historical invasions of plant health threats in Australia and New Zealand, in conjunction with knowledge of their subsequent impact, we aim to differentiate species likely to have a high impact on plant production systems from those that are likely to have a low or moderate impact in future. This will allow the current list of potential threats to be prioritised according to their expected impact. Prioritisation of plant pests and diseases, and increased knowledge of their probable invasion pathway, will facilitate effective allocation of biosecurity resources, enhancing the likelihood of early detection and prevention of the most significant plant health threats. This is particularly important for those pests predicted to be of high impact but requiring only a low propagule pressure to establish and cause this impact. Details of the methods and some preliminary results will be discussed in this presentation.