Several studies have attempted to confirm an association between a deletion/insertion polymorphism within the promoter region of the serotonin transporter gene (5-HTT) and Alzheimer's disease independent from the apolipoprotein E (APOE) varepsilon4 status. We examined this deletion/insertion polymorphism of the serotonin transporter gene in a sample of 222 consecutively recruited gerontopsychiatric patients which was divided into four different diagnostic groups: Alzheimer's disease (N=84), mild cognitive impairment (N=29), subjective cognitive complaints (N=49), depression/other psychiatric disorders (N=56) and 118 healthy, non-demented controls. The aim of this approach was to test whether the investigated polymorphism has a high enough selectivity and specificity to distinguish between the different gerontopsychiatric disorders or to differentiate genetically AD from other forms of dementia, respectively. We could not detect any significant differences in the allelic distribution of the deletion/insertion polymorphism of the 5-HTT gene between the four patient subgroups and the control group. This finding indicates that the serotonin transporter does not appear to be a major susceptibility factor in the pathophysiology of Alzheimer's disease and other psychogeriatric disorders.