Event-related potentials (ERPs) can provide valuable information about cognitive capabilities in severely brain-damaged patients. This study examined 120 patients with severe brain damage using event related potentials ERPs (N 400) to gain information about their remaining semantic processing capabilities and to contribute to differential diagnosis. Patients were classified into three diagnostic groups: patients in vegetative state (VS), patients in near vegetative state (NEVS) and patients not in vegetative state (NOVS). N400 ERPs were analyzed on an individual basis. All three groups could be differentiated by N400. While VS-patients as a group were least likely to show N400, some VS-patients (approx. 12%) showed clear semantic N400 potentials as an indication of semantic processing capabilities. Patients in NEVS showed significantly more intact semantic capabilities (76.74%) than the VS-group despite little clinical differences between the two groups. Thus, ERPs provide valuable information about patients with brain injury whose clinical conditions often do not allow a true assessment of their cognitive capabilities. Given these findings, we would espouse that both ethical and legal debate should take into account results of ERP studies of such patients.