Nonconvulsive status epilepticus (NCSE) is a type of status epilepticus (SE) lacking a predominant motor manifestation. The annual prevalence of NCSE is estimated to reach 10 to 20 cases in every 100,000 people. While almost half of all SE cases are nonconvulsive, there are several different types of NCSE: 1) epileptic absence SE, 2) epileptic focal seizure SE with consciousness disturbance (complex partial SE), 3) de novo NCSE of late onset, 4) NCSE due to acute brain injury or prolonged consciousness disturbance after convulsive SE. An electroencephalography (EEG) evaluation is necessary to diagnose NCSE. However, continuous EEG (cEEG) monitoring over at least 24 hours is preferable to detect NCSE, as cognitive disturbances due to this condition may fluctuate over time. In addition, neuroimaging techniques, such as MRI with arterial spin labeled sequences or single photon emission computed tomography (SPECT) can demonstrate hyperperfused areas in cases of focal onset. Thus, patients presenting with alternative cognitive disturbance with or without mild confusion should be evaluated using cEEG monitoring or blood flow imaging so as not to overlook treatable NCSE.