One of the most problematic aspects in the creation of spin-offs by university personnel concerns the relationship between entrepreneurial activity and research activity by researcher-entrepreneurs. The literature has expressed varying and opposing views as to the nature of the relationship but very little has been produced to empirically legitimate one position or another. The present work proposes to address this shortcoming by exploring the relationship existing between academic spin-off generation and the research performance of enterprise founders. The study investigates whether, and to what extent, scientific performance by academic entrepreneurs is different than that of their colleagues, and if the involvement in entrepreneurial activity has an influence on the individual's research activity. The research questions are answered by considering all spin-offs generated by Italian universities over the period 2001-2008 and evaluating, through a bibliometric approach, the scientific performance of founders relative to that of their colleagues who carry out research in the same field. The data show better scientific performance by the researcher-entrepreneurs than that of their colleagues and in addition, although there are some variations across fields, the creation of a spin-off does not seem, on average, to have negative effects on the scientific performance of the founders.