The paper analyzes inter- and intraregional differences in Poland in 2007 and examines the changes that have taken place within individual regions and between them since Poland’s current administrative system was introduced in 1999. The author also analyzes real regional convergence in Poland in the studied period. The author used descriptive statistics and econometric methods, along with the GDP per capita indicator. She analyzed the differences between subregions to offer a more detailed picture of development inequalities in Poland. The analysis of intraregional differences was made with the use of the Theil inequality measure for the country as a whole and by analyzing changes in the center-region relationship in selected provinces. It would be especially interesting to analyze this relationship in the context of the theory of the regional diversification of development processes, Markowska-Przybyła says, but such an analysis could not be made due to the unavailability of statistical data for half of Poland’s regions. Overall, the research carried out by Markowska-Przybyła points to increased interregional differences in Poland in 1999-2007. A β-convergence test—an estimated regression function—confirmed the existence of a regional divergence in 1999-2007, even though its statistical properties left much to be desired. Two σ-convergence tests also showed the existence of this divergence. The author concludes that processes of real regional divergence in terms of GDP per capita occurred in Poland in 1999-2007. In the studied period, in addition to growing disparities between regions, a growing diversification between subregions—Level-3 units of the Nomenclature of Units for Territorial Statistics (NUTS) routinely used by the European Union to reference the subdivisions of countries for statistical purposes—was also observed. The disparities between subregions proved to be greater than interregional differences. Intraregional inequalities revealed by the Theil inequality measure increased in 1999-2007. Development disproportions between the center and the rest of the region vary in the eight provinces analyzed. The greatest disproportions exist in Mazovia and Wielkopolska provinces, the author says, while the smallest ones are in Silesia and Łódź provinces. Lower Silesia, Łódź, Western Pomerania and Mazovia provinces showed decreased disproportions, while Silesia and Wielkopolska saw the reverse trend. In Pomerania province, center-region disproportions decreased, while disproportions between the center and the surrounding subregion increased slightly; in Małopolska province, the reverse trend was observed. The polarization of development was observed in only some provinces. No data is available on center-periphery relations in the remaining provinces, and the same goes for the position of the largest cities in these regions.