Increasing numbers of patients survive traumatic brain injury (TBI) and cardiopulmonary arrest and resuscitation and are admitted to the ICU in coma. Some of these patients become brain dead; others regain consciousness. Still others become vegetative or minimally conscious, conditions called chronic disorders of consciousness and ultimately are cared for outside the ICU. Comatose patients lack the wakefulness and awareness that distinguish consciousness from unconsciousness. Vegetative patients are awake in that they manifest sleep-wake cycles, but they are unaware of their environment and cannot respond to stimuli. Minimally conscious patients are awake, aware to a limited extent, and somewhat responsive. The diagnosis of the vegetative and minimally conscious states has been based largely on their behavioral and pathologic features, and it has been believed that vegetative patients remain in that condition permanently. Nevertheless, EEG and neuroimaging studies suggest that the traditional diagnostic approach is imprecise. Moreover, clinical investigations have revealed that some vegetative patients can become minimally conscious and that some minimally conscious patients can gain increased awareness. Few therapies for patients with chronic disorders of consciousness have been subjected to randomized trials. Furthermore, although a small number of patients have improved neurologically with or without treatment, their overall prognosis for neurologic recovery remains poor.