Ways of using different decision-aiding techniques for optimizing and evaluating radon remedial measures have been studied on a large set of data obtained from the remediation of 32 houses that had an original indoor radon level above 1000 Bq/m(3). Detailed information about radon concentrations before and after remediation, type of remedial measures and installation and operation costs were used as the input parameters for a comparison of costs and for determining the efficiencies, for a cost-benefit analysis and a cost-effectiveness analysis, in order to find out whether these criteria and techniques provide sufficient and relevant information for improving and optimizing remediation. Our study confirmed that the installation costs of remediation do not depend on the original indoor radon level, but on the technical state of the building. In addition, the study reveals that the efficiency of remediation does not depend on the installation costs. Cost-benefit analysis and cost-effectiveness analysis lead to the conclusion that remedial measures reducing the indoor radon concentration from values above 1000 Bq/m(3) are always acceptable and reasonable. On the other hand, these techniques can neither help the designer to choose the proper remedial measure nor provide information resulting in improved remediation. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.