Biological and genetic factors, as well as contextual influences, contribute to the etiology of externalizing behaviors in children and adolescents. The current project used a longitudinal design to examine how individual vulnerability for externalizing behavior is influenced by the interplay among biological/genetic and environmental factors, and how this occurs across development. We investigated the influence of dopamine receptor D4 genotype (DRD4), child temperament, and household chaos on children's externalizing behaviors using a sample of twins/triplets tested at the ages of 4 and 5 years (n = 229), including a subset of these who were tested again in middle childhood (ages 7–13 years; n = 174). Multilevel linear regression modeling demonstrated that the DRD4‐7repeat genotype, 4‐year‐old negative affectivity, and household chaos at the age of 4 years were related to 5‐year‐old externalizing behaviors. Stability in externalizing behaviors from the age of 5 years to middle childhood was demonstrated. A significant interaction between DRD4 and household chaos showed that children with no 7‐repeat DRD4 alleles had significantly higher levels of externalizing in homes with extremely low levels of parent‐reported chaos, suggesting a “goodness‐of‐fit” pattern of gene–environment interaction. These findings suggest that risk for childhood externalizing behaviors is likely multifaceted and differs across developmental periods.