OBJECTIVES The objective of our research is to give first an overview of the risks of bias in trial-based economic evaluation, and second to identify how key sources for bias can be revealed and overcome (bias-reducing strategies) in future trial-based economic evaluation in the fields of general practice and health psychology. METHODS A scoping review was performed using PubMed and the NHS Economic Evaluation data base. It was complemented with experiences of the authors. Sources of bias in trial-based economic evaluation as well as bias-reducing strategies are discussed RESULTS The different forms of bias are presented, and assigned to a particular trial phase. A distinction is made between pre-trial biases, biases during the trial and biases that are relevant after the actual trial. All potential forms of bias are discussed in detail and strategies are shown to detect and overcome these biases. CONCLUSIONS In order to avoid bias in trial-based economic evaluations, one has to be aware of all of the possible forms of bias and all stakeholders have to examine trial-based economic evaluations in a rigorous and stringent manner. Our research findings can be helpful in this examination as they provide an overview of the possible biases which researchers should take into account.