The paper deals with problems linked with calculating an equilibrium unemployment rate. Select issues concerning the theoretical aspects of the Phillips curve and Non-Accelerating Inflation Rate of Unemployment (NAIRU) estimation methods based on the Phillips curve are presented. An expectations-augmented Phillips curve was estimated using quarterly unemployment data, according to the Labor Force Survey (LFS) and core inflation excluding food and energy prices in 1995-2003. On this basis, a NAIRU level of around 12% was determined for the analyzed period using Elmeskov’s procedure. The NAIRU rate obtained in the research is similar to the equilibrium unemployment rate estimated by other authors who used unemployment inflow and outflow balance models. Poland’s NAIRU is at a high level. For example, in the United States, the corresponding rate runs at about 6%. Consequently, it is necessary to determine the causes behind this situation and take adequate measures do decrease NAIRU in Poland in the near future.