The ability to discern when actions deviate from goals and adjust behavior accordingly is crucial for efforts at self-regulation, including managing one's weight. We examined whether children with obesity differed from controls in response monitoring, an aspect of cognitive control that involves registering one's errors. Participants performed a cognitive interference task, responding to the colors of arrows while ignoring their orientations, and error-related neural activity was indexed via response-locked event-related potentials (ERPs). Compared to controls, participants with obesity exhibited significantly blunted “error-related negativity”, an ERP component linked to response monitoring. Participants with obesity also exhibited a marginally blunted “error-related positivity”, an ERP component linked to late-stage error processing, as well as in behavioral indices of cognitive control. These results suggest that childhood obesity may be associated with reduced response monitoring and that this aspect of cognitive control may play an important role in health-related self-regulatory behavior.