OBJECTIVE: To determine whether routine electroencephalography (EEG) detected electrical status epilepticus (ESE), masked by neuromuscular blockade, in comatose cardiac-arrest survivors receiving therapeutic hypothermia. DESIGN: Prospective 3-year study SETTING: Medical ICU PATIENTS: Fifty-one consecutive comatose cardiac-arrest patients treated between May 2005 and May 2008 using a standardized protocol of hypothermia with neuromuscular blockade. INTERVENTION: EEG was performed routinely as soon as possible after starting therapeutic hypothermia. EEG recordings were read by an independent neurophysiologist who was blinded to patient data. MEASUREMENTS AND MAIN RESULTS: Median body temperature at EEG recording was 33.0°C (range 32.4–33.8). ESE was found on 5 (10%) of the 51 EEG recordings: three patients had continuous rhythmic generalized spikes and two patients had continuous rhythmic focal spike-waves. Of the 17 (33%) patients who were discharged alive, 8 (8/51, 16%) had a CPC score of 1, 4 (8%) of 2, and 5 (10%) of 3. All patients with ESE died during their ICU stay. CONCLUSION: These preliminary results indicate that postanoxic status epilepticus can be masked by neuromuscular blockade during our protocol of therapeutic hypothermia. Routine EEG monitoring might be helpful in cardiac-arrest survivors receiving therapeutic hypothermia. Further studies including continuous EEG monitoring are needed to determine whether early diagnosis and treatment of ESE during therapeutic hypothermia improves the outcome.