Background: Nonconvulsive status epilepticus (NCSE) is certainly an underdiagnosed pathology with chameleonic presentation. NCSE represents a persistent change in the level of consciousness, behavior, autonomic function, and sensorium associated with continuous epileptiform electroencephalographic (EEG) changes, but without major motor signs. NCSE comprises a group of syndromes with a wide range of response to anti-epileptics from self-limiting to refractory forms. It lacks prominent motor characteristic, but may have subtle motor signs (twitching, blinking). NCSE occurs in 8 – 37% of the ICU patients. The diagnosis and treatment are not straightforward and depend on clinical presentation, etiology, EEG findings. However, it is not always clear how electrographic activity contributes to clinical impairment or to ongoing neuronal injury. EEG criteria for NCSE are – definite electrographic seizure activity with typical evolution; periodical epileptiform discharges (EDs) or rhythmic discharge with clinical sign; rhythmic discharge with either clinical or electrographic response to treatment. More difficult is when there are EDs on EEG but they do not achieve the diagnostic criteria, we must look for: subtle motor signs time-related with EDs; spatio-temporal evolution; EEG and clinical improvement with anti-epileptics. Conclusions: Thus, NCSE diagnosis requires high index of suspicion in patients with risk factors and suggestive clinical features. Availability of continuous EEG is lacking in many centers and diagnosis is delayed. Early recognition and treatment are essential to optimize therapeutic response and to prevent neurological and systemic consequences. Overdiagnosis and aggressive treatment can contribute to high morbidity and mortality.