The Santé Québec study is the most important inquiry into health yet undertaken in Quebec on life habits and the physical and psychological state of health of almost 20,000 persons aged 15 years and over living in private homes. The mental-health section of the study is situated within the tradition of socio-epidemiological inquiries. The article describes the reasoning behind the choice of mental-health indicators (psychological well-being, psychological distress, suicide thoughts and attempts, several severe psychological problems) and the measuring instruments. The study's usefulness and limits are discussed.