Background: Chronic conditions account for around two-thirds of the global burden of disease. There is a consequent interest by policy makers to address the management of these conditions. In the UK, self care constitutes a key component of the management of chronic conditions. Until recently, the cost-effectiveness evidence in favour of interventions to support self care was based on studies of limited quality with unreliable conclusions. Despite this lack of evidence, one particular intervention to support self care, the Expert Patients Programme (EPP), was rolled out across England and Wales with considerable fanfare. A randomised controlled trial (RCT) was conducted after the roll-out of the programme to establish the cost-effectiveness of this intervention. The evaluation based on this single trial concluded that the EPP was likely to be both cost saving and improving patient outcomes. Subsequent trials, including another UK based trial, have provided evidence which may be considered relevant to the decision problem. As economic evaluations should incorporate all relevant evidence, there is a persuasive argument to include some or all of this evidence. Objectives: To assess the costeffectiveness of the EPP intervention using a variety of alternative data sources and assess the impact on the results, conclusions and recommendations of including this additional evidence. Methods: Various combinations of data using surrogate and final decision endpoints were included in three analyses. Data were synthesised using techniques developed partly for this study. Results: While the single trial based analysis concluded that the EPP was almost certain to be cost-effective, synthesising these data with the other UK based data generated the result that the EPP may not be cost-effective. Indeed, the incremental cost-effectiveness ratio (ICER) of GBP 29,000 per QALY is close to the maximum of the range often quoted in the literature (GPB 20 K to GBP 30 K per QALY is commonly used as the acceptable range for the value of a QALY). Introducing non-UK data reduced the ICER to GBP 23,000 per QALY. Conclusions: Results, conclusions and recommendations of cost-effectiveness analyses can depend on what evidence is considered as relevant.