The Orbiel Valley is located downstream from the former Salsigne gold mine complex (Aude department, Occitanie), situated about 20 kilometers north of Carcassonne. Following the floods in the Orbiel Valley in October 2018, the Occitanie Regional Health Agency (ARS) consulted Santé publique France in May and September 2019 regarding the need for new epidemiological studies or updates to those already conducted. In its response, Santé publique France proposed creating a liaison committee bringing together stakeholders to discuss studies conducted and potentially to be conducted regarding health in the valley. The committee prioritized cancers as the condition of interest. In the absence of cancer incidence data at the municipal level (morbidity), it was decided to conduct, as a first step, a study of cancer mortality. Following suggestions from external reviewers, other conditions linked to metal exposure were added to this mortality study: cardiovascular diseases and neurodegenerative diseases such as Parkinson’s. This document describes the methodology for the mortality study to be implemented in the Orbiel Valley.