The central neurotransmitter serotonin plays a major role in a number of neuropsychiatric disorders. However, results from post-mortem and in vivo neuroimaging studies of the influence of age on the number of presynaptic serotonin transporters (SERT) are controversial. To provide further evidence of relevance for this ongoing discussion, SERT were imaged in 22 persons without neuropsychiatric impairment using [(123)I]2beta-carbomethoxy-3beta-(iodophenyl)tropane ([(123)I]beta-CIT) and high-resolution single-photon emission tomography (SPET). The SPET analysis method was based on magnetic resonance image co-registration in order to quantify SERT with acceptable inter- and intra-observer variability. Using this technique, we found a significant age-related decline in the thalamic/hypothalamic and midbrain/upper brainstem SERT density, which was more pronounced than that previously reported in the literature. From these results we conclude that age-related changes in SERT density need to be considered in future clinical studies.