OBJECTIVE A systematic review of somatosensory evoked potentials performed early after onset of coma, to predict the likelihood of nonawakening. The pooled results were evaluated for rates of awakening, confidence intervals, and the possibility of rare exceptions. METHODS Forty-one articles reporting somatosensory evoked potentials in comatose patients and subsequent outcomes, from 1983 to 2000. METHODS Studies were included if they reported coma etiology, age group, presence or absence of somatosensory evoked potentials, and coma outcomes. METHODS We separated patients into four groups: adults with hypoxic-ischemic encephalopathy, adults with intracranial hemorrhage, adults and adolescents with traumatic brain injury, and children and adolescents with any etiologies. Somatosensory evoked potentials were categorized as normal, abnormal, or bilaterally absent. Outcomes were categorized as persistent vegetative state or death vs. awakening. RESULTS For each somatosensory evoked potential result, rates of awakening (95% confidence interval) were calculated: adult hypoxic-ischemic encephalopathy: absent 0% (0%-1%), abnormal 22% (17%-26%), normal 52% (48%-56%); adult intracranial hemorrhage: absent 1% (0%-4%), present 38% (27%-48%); adult-teen traumatic brain injury: absent 5% (2%-7%), abnormal 70% (64%-75%), normal 89% (85%-92%); child-teen: absent 7% (4%-10%), abnormal 69% (61%-77%), normal 86% (80%-92%). CONCLUSIONS Somatosensory evoked potential results predict the likelihood of nonawakening from coma with a high level of certainty. Adults in coma from hypoxic-ischemic encephalopathy with absent somatosensory evoked potential responses have <1% chance of awakening.