The aim of the paper is to present ramifi cations in the field of family law, inheritance law and tax law which arise from the lack of recognition of registered partnerships and same-sex marriages in certain European Union Member States, such as Poland. The lack of recognition is commonly perceived as discrimination on grounds of sexual orientation, but the emphasis is usually placed on its consequences concerning human rights. In this article, the author focused on discriminatory aspects in the area of family life and personal taxation. A lack of appropriate provisions in domestic law produces negative effects affecting taxation obligations for cross-border families that concluded their marriages or partnerships abroad but cannot benefit from these institutions in certain EU Member States such as Poland. For the purpose of determining discriminatory aspects, the author analysed the domestic rules differentiating couples living in a marriage and couples not possessing the right to marry. Due to lack of case-law on tax and inheritance discrimination resulting from sexual orientation, relevant case-law of the Court of Justice of the European Union have been recalled, revealing possible violations of fundamental freedoms, including free movement of persons.