The interest in measuring social inequalities in health in Québec is relatively recent and has been hampered by the lack of socioeconomic information in the administrative databases on health. To compensate for this lack of data, a material and social deprivation index has been introduced into a dozen of these databases, making it possible to carry out numerous analyses. The present article describes the design and uses of this index and underlines the importance of social inequalities in terms of population health (healthy life expectancy), certain health and social problems (intentional or unintentional injuries, problems experienced by youth), use of health and social services at the national (hospitalization, day surgery and long-term care facilities) and local (services offered by local community service centres) levels, and allocation of public resources (physician compensation and funding of community organizations). The advantages and limitations of this index are also put into perspective, as are the possibilities it offers for research and decision-making.