About 10% of patients with severe acute psychiatric illness exhibit a cluster of motor signs (mutism, negativism, rigidity, posturing, stereotypy, staring, etc.) that are identified as the syndrome of catatonia. Catatonia responds to sedative anticonvulsant treatment (barbiturates, benzodiazepines) and to electroconvulsive therapy. These treatments raise seizure thresholds. The commonality in response indicates that catatonia, malignant catatonia, neuroleptic malignant syndrome, toxic serotonin syndrome, delirious mania, catatonic excitement, benign stupor, and oneirophrenia are best evaluated as diverse manifestations of one syndrome for clinical and neuroscience research purposes.