The present study explored the nature of attention control problems associated with ruminative traits. Experiment 1 aimed to establish the validity of a modified mental counting task that assesses individuals' ability to switch attention between internal mental representations. Reaction time and brain activity (event related potential; ERP) measures were examined, and results showed that the task was sensitive to internal attention switching effects. Experiment 2 assessed how the relationship between ruminative tendencies and switching performance differs when participants attend to neutral versus affective materials under different mood states. Although reaction-time analysis suggested that both mood condition and stimulus affectivity were not significant in altering this association, ERP analysis suggested otherwise. A significant task type×trait rumination × mood condition effect was found for switch-related ERP responses, whereby high ruminators were found to deploy more neuronal resources when switching affective materials in sad mood state.