Prolonged coma following severe head injury is a serious condition because it implies a poor prognosis. In order to assess the magnitude of this phenomenon, the authors have reviewed 135 cases of posttraumatic unconsciousness lasting more than 2 weeks, from among the entire propulation of patients with severe head injury managed in 10 years in their neurosurgical intensive care unit. The incidence of prolonged coma was 4% of all patients with acute traumatic coma, and 0.6% of all hospitalized patients with head injury. By 1 year after trauma, 30% of the patients had died, 8% survived in a vegetative state, 31% survived with severe disabilities, and 31% had made a satisfactory recovery. The early clinical picture of prolonged unconsciousness has no predictive value as to further evolution. Patients emerge from unconsciousness in consecutive steps representing the restoration of increasingly complex neurological functions; the timing of these steps is very variable and sometimes covers several months. The time distribution of recovery steps in individual cases is of limited predictive value as to outcome. The most frequent state during the recovery process is the condition of wakefulness without awareness, which should not be pronounced "permanent" earlier than 1 year after injury.