The current study tested the stress-reactivity extension of response styles theory of depression (Nolen-Hoeksema "Journal of Abnormal Psychology" 100:569-582, 1991) in a sample of high-risk children and early adolescents from a vulnerability-stress perspective using a multi-wave longitudinal design. In addition, we examined whether obtained results varied as a function of either age or sex. During an initial assessment, 56 high-risk children (offspring of depressed parents; ages 7-14) completed measures assessing rumination and depressive symptoms. Children were subsequently given a handheld personal computer which signalled them to complete measures assessing depressive symptoms and negative events at six randomly selected times over an 8-week follow-up interval. In line with hypotheses, higher levels of rumination were associated with prospective elevations in depressive symptoms following the occurrence of negative events. Sex, but not age, moderated this association. Rumination was more strongly associated with elevations in depressive symptoms following the occurrence of negative events in girls than in boys.