Although much has been written about validating DSS and other 'hard' OR models, less has been written about validating 'soft' OR models. This paper seeks to determine which contingency factors known to influence DSS validation are also important factors influencing PSM (problem structuring methods) validation. In addition, after consultation with PSM experts other contingency factors influencing PSM validation are proposed. Evidence from these PSM experts concerning the levels of influence of these factors is used to support proposals for a contingency approach to PSM validation.