Objective: ADHD is frequently detected in boys though there is no established cause. One possibility is that genes predisposing to ADHD have sexually dimorphic effects. With an aim to find out the reason for this male biasness, contribution of 14 functional polymorphisms was investigated in ADHD subjects. Method: Genomic DNA of probands, their parents, and ethnically matched controls was subjected to analysis of single-nucleotide polymorphisms and variable number of tandem repeats (VNTRs). Results: Case–control analysis revealed significant higher occurrence of DAT1 intron 8 VNTR "5R" allele (p = .028), DBH rs1108580 "A" allele (p = .027), and MAOA-u VNTR-rs6323 3R-T haplotype (p = .007) in male probands. Family-based analysis showed significant preferential transmission of Dopamine receptor D4 exon 3 VNTR-rs1800955 7R-T haplotype from parents to male probands (p = .008). Interaction between DBH gene variants and low enzymatic activity was also noticed, especially in male probands. Conclusion: Data obtained may partly answer the male biasness of ADHD. (J. of Att. Dis. 2013; XX(X) 1-XX)