Abstract: Attempts at supporting decision-making in ill-structured problem situations have focused on the development of decision support systems (DSS). In the present work the authors investigate whether these systems in fact improve decision-making. They report the results of an experiment investigating the impact of a DSS and a decision strategy on the quality of decision-making. They study the effectiveness of a DSS and a decision strategy. The positive influence of a decision strategy on the quality of decision-making is supported by the data. However, the impact of a DSS on the quality of decision-making received little or no support from the results of the experiments. The experiment suggests that teams using a DSS do not perform better than those not using it. The experiment shows that a DSS, even though its users have a positive opinion about it, does not cause them to make significantly better decisions. Decision quality does improve significantly, though, when decision-makers are guided in the way in which they structure their problem situation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>