Increasingly, atypical antipsychotic drugs are prescribed for elderly patients with symptoms of psychosis and behavioral disturbances. These symptoms often occur in patients with Alzheimer's disease, other dementias, or Parkinson's disease. As the average age of Americans increases, the prevalence of Alzheimer's disease and Parkinson's disease will rise accordingly. Although nonpharmacologic treatments for behavioral disturbances should be tried first, medications often are needed to enable the patient to be adequately cared for. Current guidelines recommend using risperidone and olanzapine to treat psychosis in patients with Alzheimer's dementia. Quetiapine and clozapine are recommended for treatment of psychosis in patients with Parkinson's disease. Additional research is needed for a recently approved agent, ziprasidone. To minimize side effects, these medications should be started at low dosages that are increased incrementally. Drug interactions, especially those involving the cytochrome P450 system, must be considered. Clozapine's potentially lethal side effects limit its use in the primary care setting. Informed use of atypical antipsychotic drugs allows family physicians to greatly improve quality of life in elderly patients with dementia and behavior disturbances.