The aim of this paper is to analyse the relationship between academic inbreeding in Portugal and research collaboration, using co-authored publications as proxies. As previous research has shown that inbreeding is detrimental for research collaborations, it is hypothesised that academic inbreeding will lead to smaller research networks and, consequently, to fewer co-authored publications outside the institution of affiliation. Relying on a large data set which merged information on academics, their inbreeding status and their publications, binomial negative and fractional models were estimated to test the hypothesis. Findings show that inbred academics have smaller research networks; while they publish most co-authored papers, the relative weight of publications written in collaboration with institutional colleagues is the highest. In contrast, non-inbred academics with foreign PhDs have larger co-authorship networks. However, they publish most single-authored papers and the weight of their international co-authorships is heaviest.