Negative discipline has been linked to childhood externalizing behaviour. However, relatively little attention has been given to the potential effect of individual personality characteristics of children and parents. Using the Five Factor Model, we examined the extent to which parents' and children's personality characteristics were related to parenting and children's externalizing behaviour in a proportional stratified general population sample (N = 599) of elementary-school-aged children. Based on Patterson's macromodel of parenting, an initial model was built, hypothesizing that the impact of parents' and child's personality dimensions on externalizing problems was fully mediated by negative discipline. Results supported a modified model that added direct pathways between parent and child personality characteristics and externalizing problem behaviour. For the mother data, as well as for the father data, children's Extraversion and Imagination were positively related to children's externalizing problem behaviours. Children's Benevolence and Conscientiousness and parents' Emotional Stability were negatively related to externalizing problem behaviours. For the mother data, maternal Agreeableness was positively related to externalizing problem behaviours too.