Previous neuroimaging work has identified anterior cingulate cortex (ACC) abnormalities in recurrent major depressive disorder (MDD), implicating a persistent underlying predisposition to depression. Error-monitoring studies in MDD, as indexed by error-related negativity (ERN), have yielded conflicting results, probably because of task differences or confounds in patient samples. ERN patterns were examined in remitted (n=19) and acutely depressed (n=17) patients, classified as a function of illness stage, and their matched controls in a go/no-go task using high-density ERPs. Results showed an abnormally larger ERN (p<.05) in remitted patients, especially in younger cases. Overall, ERN was found to decrease with age across all groups. The findings of increased ERN in remitted depression may implicate an overactive ACC associated with a hypervigilant error-monitoring system. The observed tendency of ERN reduction in a severe depressive state failed to reach statistical significance.