The article critically assesses the decision of the Polish Supreme Court in Natoniewski v. Federal Republic of Germany. It argues that the decision as such reflects contemporary international law practice. Consequently, the holding of the Supreme Court that State immunity is applicable to acts de iure imperii committed on the territory of the forum State during an armed conflict even though they may amount to war crimes seems to be correct. This conclusion also means that the Court refused to engage in law-making activity by declining to endorse interpretation, which would permit to reject State immunity by attaching superior importance to human rights. Although the article recognizes that the reasoning of the Supreme Court as well as the choice of arguments is well-balanced and convincing, it also identifies certain instances in which the Court is not entirely persuasive. In the opinion of the author, one of the most important drawbacks in the reasoning relates to the characterization of State immunity as a procedural, rather than substantive, issue.