The increasing availability of medical evidence in clinical practice was expected to improve the quality of care. However, this has not been realized. A possible explanation is that quality of care is a complex concept and needs a wider scope. Starting from the Donabedian triangle of structure, process and outcome, a framework for the analysis of quality of care is presented. The need for three types of evidence is identified and discussed: medical, contextual and policy evidence. Although the body of medical evidence is increasing, it has major flaws and gaps hampering its applicability in primary care. There is also a need to focus on the context of the medical encounter, which has been shown to influence outcome, but is still not well researched. Finally, evidence on costs, cost utility and equity needs to be considered. Taking these different aspects of evidence into account, an agenda for research in primary care is set. The analytical framework may provide new insights in the quest for improving quality of health care.