Externalizing behavior (EB) is characterized by agitation, opposition, aggression, provocation, negative thoughts and transgression of social norms (Achenbach & Rescorla, 2000). A certain level of EB is considered to be typical in preschoolers (Wakschlag et al., 2007). But persistent high levels of EB were found in subgroups of children (e.g. Calkins, Blandon, Williford, & Keane, 2007). Research has tried to identify risk factors that potentially increase the likelihood of EB. Based on the work of key leaders in this topic, Loeber and Farrington (2000) established a list according to several ecological levels, i.e. child, family, school, peer and neighborhood factors. The relations between child and family factors and EB have especially been documented in young children, while the potential contribution of school, peer and neighborhood factors was more specific in the prediction of school age children's and adolescents' EB. The current research examines the impact of two single risk factors at the child level, i.e. personality and inhibition capacities, and two single risk factors at the family level, i.e. attachment and parenting, and the impact of their cumulative effect on young children's EB incurring no distal family risk. We first review studies documenting the relations between children's EB and each of the four risk factors at the child and family levels. Second, we document research into cumulative risk with EB as an outcome. The main objective of the current study was to examine the impact of two child risk factors, i.e. personality and inhibition, and two proximal family risk factors, i.e. parenting and attachment, and the impact of their cumulative effect on later externalizing behavior among young children incurring no distal family risk. Data were collected in a longitudinal two-wave design from 161 non-referred and referred children aged three to five years at the onset of the study. All of the children were raised in families of middle to high socioeconomic status, i.e. their parents were educated to a middle to high level, had access to the job market and lived together as couples. The four risk domains were assessed at the onset of the study, while EB was rated both at the onset of the study and in the 24-month follow-up. Results confirmed that the four risk domains were each both correlates of EB and efficient at discriminating non-referred from referred children; that their combination regardless of their content (cumulative risk) provided a strong prediction of both later EB and non-referred vs referred sample membership. The results are discussed both for research and clinical purposes. ß