This paper focuses only on the comprehensive probability estimation component of pest establishment. Few studies, if any, in plant health risk assessment are based on strict quantitative analysis of the potential for pest establishment in a PRA area, and in many cases actually incorporate various qualitative, semi-quantitative and quantitative analyses (Covello and Merkhofer 1993; Wilson and Beckett 2001). Various studies often refer to the probability or likelihood of establishment and implicitly include the estimation of risk, however, there is much conceptual ambiguity in these studies in reference to the potential for pest establishment in a PRA area. Quantitative analyses to estimate the potential for pest establishment in a new environment currently free of a plant quarantine pest or disease have included multivariate techniques that estimate event probabilities estimated by multiple regression or discriminant analysis (Neter et al. 1989). Venette and Hutchison (1999) used logistic regression to determine the probability of establishment of the pink bollworm, Pectinophora gossypiella (Saunders), also based on various climatic factors, and output from the CLIMEX model. CLIMEX is a computerized system which describes the suitability of the climate for any poikilothermic organism and its potential for growth at any geographical location and/or time (Sutherst and Maywald 1985). Modelling the risk of pest establishment based on multivariate techniques or with CLIMEX is feasible, informative and provides appropriate decision-support in pest risk assessment.