OBJECTIVES: To determine the frequency of the VNTR alleles in the human dopamine transporter gene (DAT1) in the Omani population and to investigate association of the VNTR alleles with attention-deficit hyperactivity disorder (ADHD). DESIGN AND METHODS: 92 Omani children with ADHD and 110 healthy Omani subjects were genotyped for the DAT1-VNTR polymorphism in a case-control study using two independent PCR tests (one developed in our laboratory) followed by agarose gel electrophoresis. RESULTS AND CONCLUSIONS: We determined the DAT1-VNTR alleles in 202 Omani subjects. There were two common alleles (DAT1*9 and *10) and five rare ones. The DAT1*10 allele distribution was essentially the same both in the control (60.9%) and the patient group (64.6%). There was, however, a relatively higher occurrence of the DAT1*10 allele in ADHD males (69.4%) than females (55%), but this gender difference was not present in the control group (males 60%, females 62%).