The Case Study concerns the legal effects on the territory of Poland of an Austrian court decision on the establishment of a guardian for an adult person. The court case had been initiated before the Austrian court in the year 2013 and the decision in this case became final on 31 December 2013. The legal analysis concerns the sources of law that could possibly apply to the case. This leads to the conclusion that the Polish Code of Civil Procedure as introduced by the amendment of 2008 should apply to such a case. The analysis of the provision of the Polish Code of Civil Procedure leads to the conclusion that such a court decision should be recognized on the territory of Poland ipso iure. Therefore the guardian of an adult is authorized on Polish territory to deal with all the matters to which the authorization is given in the Austrian court decision.