OBJECTIVE: For new drugs to be included in appendix 1B of the drug reimbursement system, they must have proven added therapeutic value, an acceptable budget impact, and be cost-effective. To validate the latter, pharmacoeconomic evaluations have become mandatory. These evaluations should adhere to guidelines for pharmacoeconomic research. Our study evaluates: 1) the extent to which the pharmacoeconomic evaluations adherence pharmacoeconomic guidelines; 2) which guidelines are decisive in evaluating the validation of cost-effectiveness of new drugs; and 3) the impact of pharmacoeconomics in the recommendations and final decision making on drug reimbursement. DESIGN: Retrospective, descriptive study. METHOD: We examined all 1B requests for reimbursement submitted to the Dutch Health Care Insurance Board and the Medicinal Products Reimbursement Committee between 1 January 2005 and 30 September 2008, and on which recommendations on drug reimbursement have been published (n = 21). Data on adherence to guidelines, validation of cost-effectiveness, and recommendations and decision making on drug reimbursement were extracted from publicly available sources by two independent evaluators. Quantitatively and qualitatively descriptive analyses were carried out. RESULTS: Since pharmacoeconomic evaluations have become mandatory, these evaluations increasingly adhere to guidelines for pharmacoeconomic research. This was particularly true of the perspective chosen, the relevant treatment comparator and the incremental and total analyses of costs and effects of the drugs under comparison. However, cost-effectiveness of new drugs was often inadequately validated by incorrect indications for drug use, and incorrect forms of evaluation or periods of analysis. In addition, costs and effects were not always correctly analysed, nor and not enough insight was provided into the analysis model used. Partially on the basis of pharmacoeconomics, 12 new drugs are reimbursed and 9 not. CONCLUSION: Cost-effectiveness of new drugs and more valid pharmacoeconomic evaluations appear to play an ever more important role in reimbursement decision making and the pursuit of better and affordable health care.