Background: Serotonin has been linked to neuropsychiatric symptoms in Alzheimer disease, mainly agitation/aggression, depression, and psychosis. Neuropsychiatric symptoms have been associated with polymorphisms of the promoter region (5-HTTPR) and intron 2 of the serotonin transporter gene (5-HTTVNTR) or the 5-HT2A and 5-HT2C receptor genes in some but not all studies.Objective: To examine the association of the serotonin promoter, transporter, and receptor genes with neuropyschiatric symptoms in patients with Alzheimer disease. Methods:The sample included 96 patients with Alzheimer disease from the outpatient clinic of the University of California Los Angeles Alzheimer's Disease Research Center, Los Angeles. The Neuropsychiatric Inventory was used to measure neuropsychiatric symptoms, and blood samples were available for genetic analysis. Based on the literature, we hypothesized that the 5-HT2A and 5-HT2C receptor polymorphisms would be associated with agitation/aggression and psychosis and the 5-HTTPR or 5-HTTVNTR polymorphisms, with agitation/aggression or depression and anxiety. One-way analyses of variance were performed with age, ethnicity, sex, or education as covariates.Results: The 102T genotype of the 5-HT2A receptor was significantly associated with delusions (P = .045) and agitation/aggression (P = .002). We did not replicate previous associations of the 5-HT2C receptor polymorphism with psychosis or of the 5-HTTPR polymorphism with agitation/aggression, psychosis, or depression. We did not find any associations with the 5-HTTVNTR polymorphism and agitation/aggression, depression, or anxiety.