This paper analyses the inbreeding phenomena in Portuguese public universities. Inbreeding is defined as the recruitment of academics by the same institution that awarded their PhDs. Focusing on 1,217 PhD-holding Portuguese academics, belonging to four public universities and to six disciplinary areas, inbreeding is analysed in order to understand whether it might be influenced by the age of the institution and by how long ago the disciplinary area was established in a particular institution. Although a higher level of inbreeding was observed in older universities and in some of the longer established disciplinary areas, suggesting that institutional and disciplinary age play a role, it is possible to conclude that the inbreeding phenomenon is quite complex, and is influenced by other factors such as the disciplinary areas' core academic values and practices.