Catatonia is a neuropsychiatric syndrome of motor signs most frequently found in affective disorders and schizophrenia. Catatonic disorder due to a general medical condition has been added to the DSM-IV nosology. Laboratory studies, such as electroencephalography (EEG) may assist in the differential diagnosis of catatonic disorders. Twenty-six patients hospitalized on a general psychiatric unit or medical psychiatric unit received electroencephalograms (EEGs) as part of their routine care. Clinical EEG abnormalities were reported in 17 of these patients. The presence of abnormalities was associated with age greater than 40, diagnosis of neuroleptic malignant syndrome and the presence of general medical conditions associated with the development of catatonia. Although no specific EEG patterns were associated with catatonic disorder due to general medical conditions, these findings suggest that the EEG is an important tool in the evaluation of patients presenting with catatonia.