The concept of the secondary unconstitutionality of law has been appearing over the years in the adjudication of the Polish courts, adjudication of the Constitutional Tribunal and in legal literature. During this time there have been diversified contexts, in which this notion has been used. Shortly after the Constitution from 1997 entered into force, ‘secondary unconstitutionality’ was used to describe an influence of the new constitution on a so-called pre-constitutional law. Nowadays the tendency of understanding this concept is different. On the one hand, it specifies the law, which is a result of a faulty, repeating unconstitutional regulations, activity of the legislator. On the other hand, this notion is used in the situation, when as the consequence of the entry into force a judgment of the Constitutional Tribunal the new law is also unconstitutional. The aim of this article is to propose a comprehensive definition of the concept of the secondary unconstitutionality. Moreover, it will be presented a draft of the sense of this notion for the practice of establishing and applying the law in Poland.