A new contract between UK primary care practices and government was implemented in April 2004, with substantial financial rewards to general practices for achievement of standards set out in the Quality and Outcomes Framework (QOF). We aimed to review the evidence about the effects of the QOF on health care, including unintended outcomes, and equity. Relevant papers were identified by searching Medline and from the reference lists of published reviews and papers. A separate systematic literature review was conducted to identify papers with information on the impact of the framework on inequalities. All studies were observational, and so it cannot be assumed that any changes were caused by the framework. The results both for individual indicators and from different studies vary substantially. The diverse nature of the research precluded formal synthesis of data from different studies. Achievement of quality standards was high when the contract was introduced, and has risen each year roughly in line with the pre-existing trend. Inequalities in achievement of standards were generally small when the framework was implemented, and most have reduced further since. There is weak evidence that achievement for conditions outside the framework was lower initially, and has neither worsened nor improved since. Some interventions in the framework may be cost-effective. Professionals feel consultations and continuity have suffered to some extent. There is very little research about patients' views, or about the aspects of general practice not measured, such as caring, context and complexity. The evidence base about the impact of the QOF is growing, but remains patchy and inconclusive. More high quality research is needed to inform decisions about how the framework should change to maximise improvements in health and equity.