This work analyzes the relationships between behaviour disorders and psychotic symptoms in different degrees of dementia in Alzheimer's disease. In all three phases of Alzheimer's disease (moderate, moderately severe and severe dementia) in the studied group of patients a significant correlation was found between presence of hallucinations and presence of delusions. In moderately severe dementia a significant correlation was found between presence of delusions and aggression. In severe dementia significant correlations were found between hallucinations and anxiety and between anxiety and insomnia. The manifestations of these disorders, their dynamics and mutability suggest that some behaviour disorders and psychotic states in patients with Alzheimer's disease may be caused by disturbed consciousness but they are difficult to diagnose because it is not possible to assess orientation in severely dementive patients. Some of the disturbances presented by the observed patients only resemble typical psychoses but are in fact responses to other symptoms such as memory loss, disturbed orientation, visual hallucinations, disturbed recognition of places, people, their behaviour and mimicry.