The present study investigated the role of parenting stress in early adolescents' externalizing and internalizing behavior and, particularly, the moderating effect of maternal affection on these associations. The data of 992 early adolescents (x-bar[subscript age]=12.71; 454 girls) and their mothers during the transition from primary school to lower secondary school were analyzed. The results showed that when maternal affection was low, parenting stress was not related to the changes in early adolescents' externalizing or internalizing behavior. In contrast, when maternal affection was high, low parenting stress related to a decrease and high parenting stress to an increase in such behavior. The results were statistically significant and stronger for internalizing behavior; for externalizing behavior, they were marginally significant but showed the same pattern. Overall, the results support the idea that maternal affection provides a context which intensifies (rather than ameliorates) the influence of parenting stress on early adolescents' externalizing and internalizing behavior.