Using data on Poland’s 50 largest banks—ranked by Bank Miesięcznik Finansowy in June 2007—the author calculated indicators of efficiency for 23 Polish banks. These indicators were calculated for 2006 according to a key Data Envelopment Analysis (DEA) model known as the SE-CCR. On the basis of data on the banks’ shareholding structure by country of origin and type of ownership—as well as data on when the banks were established—the author checked if individual groups of banks differed from one another in the average level of efficiency. Guzik used the Kruskal-Wallis test to this end. He also developed a model to explain the relationship between efficiency in the sense of CCR super-efficiency and the ownership structure of banks and their age. Overall, the paper shows that privately held banks controlled by foreign shareholders and established after 2000 are far more efficient than banks owned by domestic shareholders and established before 2000, especially if they are controlled by the state.