The health system is a social determinant of health. Although not the most important determinant of health, the health system's potential contribution to reducing social inequalities in health should not be underestimated. Due to its characteristics, primary health care is well placed to attain equity in health. To make progress in achieving this goal, the main measures to be considered are the removal of barriers to access to services, the provision of care proportionate to need, and engagement in intersectoral work. This article reviews the background and framework for action to tackle social inequalities in health and provides a summary of the primary health care actions that could help to reduce social inequalities in health and are mentioned in the most important national and international documents on health policy. We hope to stimulate debate, promote research in the field and encourage implementation. The proposals are grouped in the following five intervention lines: information systems; participation; training; intersectoral work; and reorientation of health care. Each intervention is ordered according to its targets (population and civil society; primary health team; health center and health area management; and health policy decision-makers).