OBJECTIVE: To assess the incidence, quantified EEG characteristics, and prognostic significance of "burst-suppression with identical bursts" and to discuss potential pathophysiological mechanisms. METHODS: Burst-suppression EEGs were identified from a cohort of 101 comatose patients after cardiac arrest, and from our complete database of 9600 EEGs, since 2005. Patterns with and without identical bursts were classified visually by two observers. Of patients after cardiac arrest, outcomes were assessed at three and six months. Identical and non-identical burst-suppression patterns were compared for quantified EEG characteristics and clinical outcome. Cross correlation of burstshape was applied to the first 500ms of each burst. RESULTS: Of 9701 EEGs, 240 showed burst-suppression, 22 with identical bursts. Identical bursts were observed in twenty (20%) of 101 comatose patients after cardiac arrest between a median of 12 and 36h after the arrest, but not in the six patients with other pathology than cerebral ischemia, or the 183 with anesthesia induced burst suppression. Inter-observer agreement was 0.8 and disagreement always resulted from sampling error. Burst-suppression with identical bursts was always bilateral synchronous, amplitudes were higher (128 vs. 25μV, p=0.0001) and correlation coefficients of burstshapes were higher (95% >0.75 vs. 0% >0.75, p<0.0001) than in burst-suppression without identical bursts. All twenty patients with identical bursts after cardiac arrest had a poor outcome versus 10 (36%) without identical bursts. CONCLUSION: "Burst-suppression with identical bursts" is a distinct pathological EEG pattern, which in this series only occurred after diffuse cerebral ischemia and was invariably associated with poor outcome. SIGNIFICANCE: In comatose patients after cardiac arrest, "burst-suppression with identical bursts" predicts a poor outcome with a high specificity.