THE male predominance of externalizing behaviors suggests that the X-linked androgen gene might be involved. Since the shorter alleles of the CAG and GGC polymorphisms of the AR gene are associated with increased gene expression we sought to determine whether they were also associated with externalizing behaviors. We examined 302 subjects consisting of Tourette syndrome probands and controls. ANOVA showed a significant association between the AR haplotypes and ADHD (p < 0.0001), conduct disorder (CD; p < 0.017), and oppositional defiant disorder (ODD; p < 0.004) with the lowest scores in those with the longer alleles at both polymorphisms. These results suggest that genetic variation at the human AR gene plays a role in human externalizing disorders.