The authors describe three patients presenting several episodes of paralysis of the motor and sensory cranial nerves and discuss possible aetiological factors. The paralytic attacks were regressive and were repeated at irregular intervals over a period of several years. It was confirmed that no local or general cause for the symptoms existed and the conclusion was reached that they were part of an autonomous clinical syndrome of unknown aetiology. Other cases have been reported in the published literature in which a non-specific inflammatory mechanism is suggested but no biological or pathological basis exists to support this physiopathological hypothesis. The clinical syndrome follows a benign course, the paralysis being regressive and the affection remaining confined to the peripheral nervous system of mesencephalic origin.