The phenomenology of Behavioral and Psychological Symptoms of Dementia (BPSD) occurring in the Alzheimer's disease and related syndromes remains not well known. The goal of this study was to assess the role of disorders of personality, psychiatric disorders and home environment in the occurence of the BPSD; 99 inpatients from a short-term Alzheimer unit were included in the study. BPSD were assessed by the NeuroPsychiatric Inventory, the severity of dementia by the MMSE. Previous somatic, psychiatric and personality disorders were evaluated by a semi-structured interview of the family, and classified according to the A, B and C groups from the DSM-IV. Eighty eight percent of the patients presented at least one BPSD. The patients whose the main caregiver was a spouse appeared to be more aggressive. Sixty seven per cent of the patients presented with former disorders of personality; they were more delirious, more anxious, more irritable and suffered more disorders of appetite. Each type of personality disorder modified the phenomenology of the BPSD. The severity of dementia does not seem sufficient to explain the occurrence of BPSD. Other factors seem to play a dominating part such as the previous disorders of personality and psychiatric antecedents. However, the exact links between disorders of personality, psychiatric antecedents and BPSD remain difficult to specify.