Abstract Background Informal patient payments continue to exist in many European countries. These payments might take various forms but can be broadly defined as any payments in addition to formal fees determined by the terms of entitlement. Poor health system governance is considered one of the main factors contributing to their presence, although different aspects of governance might be relevant in each country. The aim of this study was to develop an assessment instrument to help identify gaps in health system governance that contribute to informal patient payments. Methods The study has been performed in 2022-2023 in three stages. In the first step, relying on the TAPIC framework and available literature on informal patient payments, we developed a list of questions for each domain of governance: Transparency, Accountability, Participation, Integrity, Capacity. In the second step, the questionnaire was assessed by external experts to ensure it covers the full range of relevant aspects. We then applied the instrument to three European countries, i.e. Denmark, Greece, and Poland, where informal payments differ in scale. Results The developed instrument includes 22 questions in the five TAPIC domains. They particularly refer to the role of governance in eliminating underlying reasons for informal patient payments (poor quality of health care) and effective penalization of these payments. The application of the instrument showed that in two countries where informal payments are more common, i.e. Greece and Poland, quality and waiting time guarantees are poorly defined, monitored, and incentivized, while existing mechanisms only penalize payments proven to be bribes. Conclusions There is a broad range of health system governance aspects that can be directly or indirectly linked to informal patient payments. The proposed instrument can facilitate the development of long- and short-term policies to eliminate informal payments in European countries. Key messages • Policy makers need to take greater account of the role of governance in ensuring health care quality to eliminate informal patient payments. • The lack of mechanisms to penalize all types of informal payments may contribute to the commonness of these payments in Europe.