PL
The aim of the article is to verify the impact of fiscal transparency on the quality and reliability of public finance sector data which in turn are the basis for formulating conclusions on the effectiveness of fiscal policy and the sustainability of public finance. The article identifies and provides examples of the primary areas that impair fiscal transparency in Poland, particularly: the scope of public finance sector, the extra-budgetary institutions and fiscal rules. In conclusion the author underlines that the findings based on published budgetary data can be subject to a significant error.