In daily hospital activity a frequent observation is that of patients in conditions of acute global suffering of the central nervous system due to a primary cause or symptomatic of other diseases. This condition shows an alteration of the state of consciousness, which involves three possible semeiologic manifestations: delirium (acute confusional state), acute confusional state associated with psychomotor underactivity and coma. The possible causes of an acute encephalopathy (AE) are: metabolic, iatrogenic and toxic, infective, primary neurologic, surgery-related and others. Diagnostic-therapeutic routes to be followed by emergency room doctors and neurologists dealing with AE are defined.