A workshop on late blight simulation was held 13-16 April 2004 at the International Potato Center (CIP), Lima, Peru. Participants included Jorge Rivadeneira (INIAP, Instituto Nacional de Investigaciones Agropecuarias, Ecuador), Peter Kromann and Arturo Taipe (CIP, Ecuador), Jeni Barboza, Henry Juarez, Wilmer Perez and Rubi Raymundo (CIP, Lima), and Tomas Melgarejo (UNALM, Universidad Nacional Agraria La Molina, Lima). Jorge Andrade-Piedra (Cornell University) and Greg Forbes (CIP, Lima) coordinated the workshop. The participants became familiar with a version of the LATEBLIGHT simulator (Bruhn and Fry, 1981, Phytopathology 71:612–616) adapted for the tropical highlands by Andrade-Piedra et al. (in preparation). The topics included collection of data in the field, preparation of data for the simulator, selection of parameters, validation of data produced by the simulator and analysis of results.