The main purpose of the article is to analyse the category of metaphysical boredom. It is understood as a principle of existence, an irremovable feature of existence (defined mainly in Søren Kierkegaard’s philosophy). This kind of boredom is very close to the category of romantic boredom which is an essential element of the romantic worldview and part of romantic existence. First of all, it appears to be a border experience (in the existential and cognitive sense) which constitutes the identity of the romantics. It denotes a state in which a question may be asked about the sense of existence. This leads to a description of the world in which existence is treated as nothingness. In this case boredom turns out to be a confrontation with the fact that one is condemned to existence. The bored subject has the feeling of being imprisoned in its own existence and suspended in the world defined as an abyss in which one cannot fi nd any point of support. It is in boredom that one embraces the whole existence: the bored subject sees a possibility of not existing, it perceives the world the way it is, as insignifi cant, fragile and chaotic. Słowacki and Witkacy were two great writers who wanted to explore boredom. In their works and biographies we can find examples of such boredom — showing very clearly that existence is infected by nothingness and the world is deprived of any ordering principles. A detailed analysis of the writers’ letters (mostly Słowacki’s letters to his mother and Witkacy’s letters to his wife) reveals a picture of boredom that is absolute, total, all-embracing and irremovable. Boredom is neither a transition state, nor a temporary mood. It does not exist at the emotional level. Boredom pervades everything; it becomes “air”, an irremovable element of existence. That is why one has to understand it as metaphysical boredom: as a feature of existence, a principle of existence and nothingness that is everywhere. Both the biographies of the two writers (which, as the letters show, were a constant fight with boredom) and their works (many of which were dedicated to boredom) are extremely important contributions to the discussion about the notion of boredom.