Evidence based medicine has been a topic of considerable controversy in medical and health care circles over its short lifetime, because of the claims made by its exponents about the criteria used to assess the evidence for or against the effectiveness of medical interventions. The central epistemological debates underpinning the debates about evidence based medicine are reviewed by this paper, and some areas are suggested where further work remains to be done. In particular, further work is needed on the theory (...) of evidence and inference; causation and correlation; clinical judgment and collective knowledge; the structure of medical theory; and the nature of clinical effectiveness. (shrink)