Systematic surveillance of population health in relation to occupational activity is still underdeveloped in France. The objective of this methodological guide is to facilitate and promote epidemiological surveillance in the workplace through, on the one hand, the systematic epidemiological analysis of mortality by cause and, on the other hand, the investigations to be conducted when clusters of cases are suspected in one or more companies(s). This guide was designed to provide occupational physicians (and relevant stakeholders) with a description of the essential data that must be systematically collected to carry out, without undue difficulty: - systematic epidemiological surveillance of mortality (using administrative data) or the incidence of a disease within the workplace (provided that complete administrative data and comprehensive medical data on incident cases are available); - an investigation of a spatio-temporal cluster of cases. Readers will find in this guide the main steps for conducting mortality and incidence studies: establishing a cohort of employees, collecting mortality and incidence data, and describing the methods for calculating standardized mortality ratios (SMR) and incidence ratios (SIR). Two mortality studies and one incidence study are presented as examples. (R.A.)