Behavioral disturbances and psychiatric disorders are common in persons with Alzheimer's disease and other dementias. Personality changes are often the earliest sign of dementia; behavioral disturbances and psychiatric comorbidity generally occur in the middle and later stages of the disease. At some time during the course of their illness, most patients with dementia exhibit behavioral disturbances or signs of psychiatric comorbidity. The presence of a comorbid psychiatric condition increases the likelihood that the patient will have behavioral disturbances. Although the rate, severity, and effects of behavioral disturbances can be influenced by pharmacologic and behavioral management, the efficacy of these interventions often is modest.