On June 11, 2019, the occupational physician at a company specializing in chemical research and innovation reported to the Île-de-France Regional Health Agency an unusually high number of thyroid disorders among staff at one of the company’s research laboratories located at a site in the department of Seine-Saint-Denis (93). In collaboration with the Île-de-France Direccte, the Paris Poison Control Center, the Thyroid and Endocrine Tumors Unit at the Pitié-Salpêtrière University Hospital (Paris), and the Occupational Health and Environment Directorate of Santé publique France, the Santé publique France Regional Unit in Île-de-France conducted an investigation to identify and document cases, objectively assess the excess of cases, and determine whether exposures likely to be linked to this excess were present, if applicable. The investigative approach adopted is based on the methodological guidelines developed by Santé publique France for the assessment and management of spatio-temporal clusters of non-infectious diseases in the workplace. This process follows a multi-step decision tree. Based on the health and environmental data collected at each stage, a decision is then made on whether to continue the investigation. In total, two cases of thyroid cancer diagnosed incidentally and twelve cases of thyroid nodular abnormalities diagnosed following systematic screening were identified among the staff of the laboratory, which specializes in polymer formulation. Calculation of the standardized incidence ratio showed that the number of thyroid cancer cases was significantly higher than expected based on national incidence data. However, the very small size of the study population makes the number of expected cases difficult to interpret and does not allow for a conclusion regarding excess risk. Furthermore, environmental investigations and available scientific data did not identify, within the employees’ occupational environment, exposures that could explain the observed cases of thyroid cancer and thyroid nodular abnormalities. Given the methodological considerations and the results of the health and environmental investigations, it was deemed useful to supplement this work with an analysis of the feasibility of expanding the scope of the investigation. This feasibility study will explore various avenues, and its conclusions will help determine whether it is appropriate to implement the expanded investigation. Furthermore, following the investigation, a number of recommendations have been formulated. These include, in particular—for occupational medicine—continuing to monitor all new cases of cancer while ensuring that the sociodemographic and clinical data essential for any potential future epidemiological study are carefully collected. It is also recommended that the company continue monitoring exposure to chemicals through individual tracking of employees and establish a rigorous system for recording employees’ sociodemographic and occupational data in order to have the necessary and sufficient information available to conduct an epidemiological study, if needed.