The state of the art on the issue of sex differences in research efficiency agrees in recognizing higher performances for
males, however there are divergences in explaining the possible causes. One of the causes advanced is that there are sex differences
in the availability of aptitude at the “high end”. By comparing sex differences in concentration and performance of Italian
academic star scientists to the case in the population complement, this work aims to verify if star, or “high-end”, scientists
play a preponderant role in determining higher performance among males. The study reveals the existence of a greater relative
concentration of males among star scientists, as well as a performance gap between male and female star scientists that is
greater than for the rest of the population. In the latter subpopulation the performance gap between the two sexes is seen
as truly marginal.