INTRODUCTION: Nonconvulsive status epilepticus (NCSE) is a condition involving seizures without convulsions; it is usually characterized by altered consciousness and behavioral and vegetative abnormalities. Owing to the nonspecific symptoms, NCSE is often overlooked, especially in neurological intensive care unit (NICU) patients. Therefore, we investigated the etiology, clinical features, electroencephalographic (EEG) changes, treatment options, and outcomes of NCSE in NICU patients with altered consciousness. METHODS: This study retrospectively collected the data of 20 patients with altered consciousness in the NICU. NCSE diagnoses were established by the treating neurologist who had been trained to recognize nonspecific clinical signs and recognize complex EEG changes. RESULTS: We identified 20 patients (43.95±20.70 years) with clinical signs and EEG findings consistent with NCSE; 9 were female. All the patients suffered from altered consciousness. Five patients had established epilepsy. NCSE was attributed to acute pathological conditions. The underlying cause of NCSE was intracranial infection in 6 patients (30%), cerebrovascular disease in 5 patients (25%), irregular use of epilepsy drugs in 2 patients (10%), immune-related inflammation in 1 patient (5%), other infections in 4 patients (20%), and unknown cause in 2 patients (10%). Fifteen patients had diffused, and five patients had temporal focal EEG abnormalities. Six of 20 NCSE cases (30%) resulted in death. All the patients, except for the patients who died, received anticonvulsant therapy and their altered conscious state was promptly altered. CONCLUSION: The clinical symptoms of NCSE without convulsions are often obscure and difficult to detect. NCSE can cause serious consequences and even death. Therefore, for patients with a high clinical suspicion of NCSE, continuous EEG monitoring is needed to quickly identify this condition and promptly start treat them.