In 1997, the French Ministries of the Environment and Health commissioned a detailed radioecological analysis of the Nord-Cotentin region in response to public concern about radiological risks associated with local nuclear facilities. This work was entrusted to the Groupe Radioécologie Nord-Cotentin (GRNC), a working group of experts from various origins (industrial facilities operators, public institutions, monitoring agencies, public interest and citizens groups, foreign experts). An epidemiology investigation in 1995 had reported an excess of two radiation-induced leukemia cases in an area near a nuclear reprocessing plant, a finding that attracted great interest in France, and which stimulated the need for further investigation. After the publication of its report in 1999, the GRNC was again commissioned to perform, inter alia , a corresponding assessment on the chemical releases of the local nuclear facilities. This second stage is now achieved and has revealed important similarities as well as some important differences between radiological and chemical risk assessments when applied to the specific case of the Nord-Cotentin nuclear facilities. Due to the considerable amount of work and results of the GRNC, the purpose for this article is to briefly describe the main developments of the risk assessment methodology followed by the GRNC in both cases, to detail some of the main results and to identify and explain, at each step, the similarities and the differences. The whole technical documents that support these works are available on the Internet at 〈http://www.irsn.fr/nord-cotentin/〉.