Pathogenic micro-organisms receive muchattention due to their potentially harmfuleffects on human, animal or plant health.Over the past few decades, this attentionhas grown due to the emergence of new(and known) infectious diseases inducinglocal epidemics as well as worldwide pandemics.Along with the research and diagnosisof those etiological agents, (bio)safetyconcerns have highlighted the biologicalrisks associated with their deliberate usein laboratories, animal facilities and productionplants, and their transboundarymovements (import and export). This hasled to their categorisation into risk groupsand the elaboration of classification lists.Current international classification systemsrely on criteria defined by the WorldHealth Organisation, which cover the severityof the disease the micro-organismmight cause, its ability to spread and theavailability of prophylaxis or efficient treatment(1). Animal pathogens are classifiedaccording to the definitions of the WorldOrganisation for Animal Health, which alsoconsider economic aspects of disease (2).Evolution of scientific knowledge will demandregular updating of classificationlists. This paper describes the Belgian riskclassification system and the methodologythat was used for its peer-reviewed revision(with a focus on animal pathogens).