Background: The weaknesses of informal reviews are seen to derive from failures in their procedural specification and the tendency of the (thus) undisciplined reviewer to construct idiosyncratic theories and marshall the evidence accordingly, or to be chaotic or negligent in identifying the evidence. However, critiques of conventional systematic review methodology have focused on both the nature of the truth claims it can make and its inappropriateness for some forms of review question.

Objectives: To propose Critical Interpretive Synthesis (CIS) as a way of synthesising diverse forms of evidence and illustrate its application to a review on access to health care.

Methods: CIS draws both on traditions of qualitative research inquiry and on systematic review methodology, and can be used to synthesise qualitative and quantitative forms of evidence. It is explicitly oriented towards theory building; proposes an iterative and dynamic approach to question formulation, searching, and selection of materials for inclusion in reviews; treats the literature as warranting critical scrutiny in its own right by questioning its underlying assumptions; and achieves synthesis through a dialectic process between evidence and theory. It is explicitly reflexive about the 'authorial voice' that produces the account of the evidence.

Results: Using CIS allows an identification of the limitations of studies of utilisation as a guide to explaining inequities in access to health care. It also allows the generation of a conceptual model that emphasises 'candidacy' as the core organising construct, and recasts access as highly dynamic and contingent, and subject to constant negotiation.

Conclusions: CIS offers a way of synthesising diverse forms of evidence. It does not claim to be an inherently reproducible process or product, but can be defended on other grounds and may provide an important complement to more conventional forms of systematic review.