The interaction between evidence-based medicine and doctors' duty of care to patients is complex. One the one hand, there is surely an obligation to take account of the best available evidence when offering health care to patients. On the other hand, it is equally important to be aware of important shortcomings in the processes and practices of evidence-based medicine. There are tensions between the population focus of evidence-based medicine and the duties that doctors have to individual patients. Implementing evidence-based medicine may have unpredictable consequences upon the overall quality of health care. Patients may have a range of reasons for preferring one form of treatment over another, not all of which are captured by current formulations of evidence. This paper examines these issues, using relevant examples from evidence-based medicine.