Inclusion Criteria:

• Probable Alzheimer's disease (NINCDS-ADRDA criteria), with MMSE score of 5-26 inclusive
• Clinically significant agitation for which 1) a medication is needed; 2) score ≥ 4 on the Neuropsychiatric Inventory (NPI) agitation domain; 3) more than 2 agitated behaviors per week as assessed on the NPI
• Availability of primary caregiver, who spends several hours a week with the patient and supervises his/her care, to accompany the patient to study visits and to participate in the study
• Sufficient fluency, of the patient and caregiver, in written and spoken English or Spanish to participate in study visits, neuropsychological testing, and other outcome assessments
• Stable treatment for AD with cholinesterase inhibitors and/or memantine

Exclusion Criteria:

• Meets criteria for Major Depressive Episode by DSM-IV criteria
• Presence of a brain disease that might otherwise fully explain the presence of dementia, such as extensive brain vascular disease, Parkinson's disease, dementia with Lewy bodies, traumatic brain injury, or multiple sclerosis
• Psychosis (delusions or hallucinations) requiring antipsychotic treatment in the opinion of the study physician
• Treatment with citalopram is contraindicated
• Failure of past treatment with citalopram for agitation after adequate trial at a minimally accepted dose (greater than or equal to 20mg/day)
• Treatment with a medication that would prohibit the safe concurrent use of citalopram, such as MAO inhibitors
• Need for psychiatric hospitalization, or acutely suicidal
• Current participation in a clinical trial or in any study that may add a significant burden or affect neuropsychological or other study outcomes
• Current treatment with antipsychotics, anticonvulsants, other antidepressants (other than trazodone, less than or equal to 50 mg per day at bedtime), benzodiazepines (other than lorazepam), or psychostimulants
• Any condition that makes it medically inappropriate or risky for the patient to enroll in the trial