Jurisprudence interprets “legislative unlawfulness” as an unlawful act on behalf of the legislator, which may consist in passing a legislative act that violates the legal order, i.e. the axiological grounds of the legal system and the way the body of laws is formed, e.g. the hierarchy of the sources of law, failure to promulgate a legislative act in nonfeasance despite an existing obligation to do so, which may result in emergence of legal loopholes. As indicated by the judgements of the Polish Constitutional Court, the legal security of an individual is bound to the consistency and certainty of law, and allows the individual to forecast, plan rationally their activities in accordance with the predictability of what the state authorities do. Therefore, an individual should be certain of the law (i.e. experience legal security) when undertaking activities in line with the binding legal order, that is to be able to determine confidendy the legal effects of such activities. Hence, each instance of legislative unlawfulness violating the legal order instantaneously violates the principle of trust for the state and its established law and threatens the individuals legal security. Legislative unlawfulness may occur when: the legislator establishing a normative act violates the rules of law stemming from the principal rule of the democratic state of law; when the sentences of the Polish Constitutional Court are not executed. The Court derogates a legal article and the legislator ceases to establish a new norm regulating a particular matter within a suitable time (legislative nonfeasance) leading to the emergence of a legal loophole. The objective of the paper is to discuss the issue of legislative unlawfulness in Poland (with the major focus on the two cases mentioned above) in the context of the individuals legal security, followed by an attempt to formulate conclusions de lege lata and de lege ferenda.