The vegetative state is a clinical condition of complete unawareness of the self and the environment. It is accompanied by sleep-wake cycles, with either complete or partial preservation of hypothalamic and brain-stem autonomic functions. In addition, patients in a vegetative state show no evidence of sustained, reproducible, purposeful, or voluntary behavioral response to visual, auditory, tactile, or noxious stimuli. They show no evidence of language comprehension or expression; have bowel and bladder incontinence; but have variably preserved cranial-nerve and spinal reflexes.

Being in a vegetative state is associated with greatly elevated mortality rates. The requirement of a tracheostomy or ventilator is further associated with even higher mortality beyond the baseline for someone in the vegetative state.