The dopamine transporter (DAT) is a functional element of the dopaminergic synapse in the brain. Its primary role is the regulation of dopamine (DA) availability by forward and reverse transport of DA from and to the synaptic cleft by which extracellular DA concentrations are being regulated. The DAT gene and especially the DAT 10/10 genotype have been intensively discussed as a candidate for several neuropsychiatric disorders including attention-deficit-hyperactivity disorder (ADHD). We found recently that the DAT 10/10 genotype is associated with increased levels of CSF DA and is present more frequently in HIV-infected individuals than in uninfected subjects, suggesting that personality traits related to this polymorphism may increase the risk of acquisition of HIV. In this article, we review studies on the DAT 10/10 genotype and the association with ADHD and its endophenotypes, express concerns on the reported DA neurochemistry in ADHD and discuss consequences of the DAT 10/10 genotype on the epidemiology of HIV infection.