The range of allele frequency variation in humans for any locus that may have functionally important genetic variation needs to be documented. Therefore, we tested two polymorphisms at the serotonin transporter protein locus (SLC6A4) in samples from seven specific populations from five continental regions. We studied the promoter polymorphism which is reported to have functional significance and to be associated with anxiety- and depression-related phenotypes [Lesch et al., 1996: Science 274:1527-1531], and the intron 2 VNTR polymorphism [Lesch et al., 1994: J Neural Transm 95:157-162]. Allele frequencies for both systems show significant global variation, and consequently so do haplotype frequencies. Linkage disequilibrium varied among the populations, being absent in some and highly significant in others. These differences further document a large potential for population stratification in association studies of either of these SLC6A4 polymorphisms.