The purpose of this study was to examine self-regulation as a mediator of the relation between family functioning and externalizing behaviour in 731 low-income children (M age = 41 months) across three time points. Specifically, this study focused on whether chaos in the home and positive behaviour support were indirectly related to externalizing problems through their influence on inhibitory control. The primary findings were as follows: (a) chaos in the home at age 3 years was indirectly related to externalizing behaviour at age 5.5 years through children's inhibitory control at age 4 years, and (b) positive behaviour support at age 3 years was indirectly related to externalizing behaviour at age 5.5 years through inhibitory control at age 4 years. Implications of these findings and directions for future research are discussed.