A 41-year-old man presented with reduced consciousness and severe autonomic dysregulation. Besides an increased creatine kinase of 978 U/l, no other abnormalities were found. After excluding infectious or autoimmune causes, drug withdrawal and serotonergic syndrome, malignant catatonia was suspected. Catatonia is a neuropsychological disorder, characterised by various movement disorders and the inability to react to external stimuli. A malignant subtype of catatonia is associated with lifethreatening autonomic instability. The patient was not reactive to treatment with benzodiazepines. Electroconvulsive therapy (ECT) was commenced. After a total of 13 ECT treatments his catatonic state resolved, including the autonomic dysregulation. The exact pathophysiological mechanism of malignant catatonia is unknown. Dysregulation in cortical-subcortical circuits, neurotransmitters and synaptic transmission may play an important role. Early recognition of malignant catatonia is essential. First-line treatment is lorazepam. In case of life-threatening conditions or no response to benzodiazepines, the patient should be treated with ECT. © 2017, Netherlands Society of Intensive Care. All rights reserved.