This study employs data envelopment analysis (DEA) to evaluate relative efficiency of a sample of 54 Italian and 30 Polish public universities for the period between 2001 and 2011. The examination is conducted in two steps: first unbiased DEA efficiency scores are estimated and then are regressed on external variables to quantitatively asses the direction and magnitude of the impact of potential determinants. The analysis shows the strong heterogeneity in the efficiency scores within each country, more pronounced than the difference in average efficiency scores between countries. There is evidence that efficiency is determined by revenues’ and academic staff’s structure: competitive versus non-competitive resources, and the number of professors among academic staff. The study also explores the variation of efficiency and productivity over time, and reveals that while pure efficiency change was similar between the two countries, the efficiency frontier improved more in Italy than in Poland.