Numerous lines of evidence have shown that attention deficit hyperactivity disorder (ADHD) is a highly heritable disorder, whether it is considered as a category or a dimension. We tested for an association between the dopamine transporter gene (DAT1) and ADHD considering the disorder as categorical as well as a continuous trait. Genotypes for the DAT1 variable number of tandem repeat (VNTR) alleles, along with Brown Attention Deficit Disorder Scale (BADDS) and Wender Utah Rating Scale (WURS) scores were available for 152 adult ADHD patients. In 72 of these patients DNAs from at least one parent were accessible to perform a family-based analysis (FBAT). The mean quantitative trait values of the whole sample of singleton patients were compared among the specific genotype groups using ANOVA. The family-based analysis did not reveal any association between DAT1 alleles and ADHD either when it was considered as a dichotomous trait (Z = 0.16, p =.86) or as a continuous trait (Wender Scale Z = -1.67, p =.09; Brown ADD Scale Z = 0.28, p =.77). No significant differences were detected in the mean symptom scores among the specific genotype groups. The results from our study do not support a major role for the DAT1 VNTR alleles in our sample of adult ADHD. In view of several positive reports in child ADHD, more work is required to elucidate the potential role of the DAT1 VNTR as a risk factor in ADHD.