This workshop offers a critical examination of the use of patient self-reports in pharmacoeconomic evaluations. This session is directed at individuals in pharmaceutical firms, CROs, and consultancy companies who are responsible for the design and conduct of pharmacoeconomic evaluations. The workshop advances recent research by concentrating on how the method of data collection in prospective clinical economic evaluations may influence study findings. Scant attention has been paid to the fact that the high level of internal validity found in prospective studies may be compromised by the application of inappropriate methodologies to data collection. Particular attention in this workshop is placed on how validity may be affected by the elapsed time between admission and self-reporting, salience of a treatment event and perceived social desirability of a condition. As part of this workshop we will highlight areas where estimates based on patient self-reports lead to either reliable or suspect values. In particular, we examine the areas of hospitalization, outpatient consultations, medication use and indirect costs. The impact that patient self-reports have on cost effectiveness ratios is also discussed. Attendees at this workshop will gain an understanding of current methodological shortcomings in this area and researchers and readers of pharmacoeconomic studies will gain the skills necessary to better design studies and evaluate the validity of, and potential for bias in cost effectiveness analyses.