The vegetative state is a clinical condition of complete unawareness of the self and the environment, accompanied by sleep-wake cycles, with either complete or partial preservation of hypothalamic and brain-stem functions. If the vegetative state has continued for at least 1 month, it is defined as a persistent vegetative state. In this study we report the results of clinical, electrophysiological and imaging study of four patients with persistent vegetative state induced by hypoxic or anoxic encephalopathy.