In this paper the authors carry out an analysis of the effectiveness of European Union economic cohesion policy. It was done from a perspective of one of the most economically depressed regions in Poland and in the EU – the Warmia and Mazury voivodeship. The economic effectiveness of the cohesion policy is measured by analysing the reduction of disparities between regions with the lowest level of economic development and regions that are more developed. The aim of the research was to evaluate the rate of economic growth in Warmia and Mazury and in Poland. The basis of the evaluation was a comparative analysis of the GDP per capita growth rate against selected countries and regions of EU in the years 1995–2010. Studies have shown that compared with the regions and countries of the EU, the analysed voivodeship was characterized by a relatively rapid rate of economic growth. At the same time, however, the economies of the most developed regions of Poland were growing faster. Consequently, the EU cohesion policy in the Warmia and Mazury region has been found to be effective in comparison with other countries and regions of the EU, but questionable in the national dimension.