The present paper investigates the efficiency of the Polish banking industry between 1997 and 2001. Our preferred methodology is Data Envelopment Analysis, which allows us to distinguish between cost, allocative, technical, pure technical, and scale efficiency. Additionally, we perform a number of tests to investigate whether domestic and foreign banks come from the same population. Finally, we attempt to shed light on the determinants of efficiency. Our results indicate that bank efficiency has not improved during the years analyzed. Whereas greenfield banks have achieved higher levels of efficiency than domestic banks, foreign banks that acquired domestic institutions have not succeeded in enhancing their efficiency.