Psychological disturbances in 49 most severely compromised Guillain-Barré syndrome patients were prospectively studied by a semistructured interview and assessed by repeat psychiatric examination during the patients’ stay in the neuro-intensive care unit (ICU). Additional information was obtained from attending physicians, nurses and relatives. Anxiety (82%), acute stress disorder, depressive episodes (67%) and brief reactive psychosis (25%) were observed, with oneiroid psychosis (14%) among the latter. Psychotic episodes were strongly associated (p < 0.001) with severe tetraparesis, artificial ventilation and multiple cranial nerve dysfunction. CSF protein concentration was also correlated with the occurrence of psychotic symptoms. Patients themselves experienced loss of communication to be the most difficult condition to cope with. Fifty-five percent explicitly felt reassured by the environment of the ICU and 90% described contact with relatives to be most helpful. Our data suggest that motor deprivation and loss of communication are the conditions most closely connected with the occurrence of psychotic symptoms. Therapeutically, continuous psychosocial support and psychopharmacological measures may both be valuable tools to ameliorate distress.