Attention deficit hyperactivity disorder (ADHD) is a common, highly heritable, neurodevelopmental disorder with onset in early childhood. Genes involved in neuronal development and growth are, thus, important etiological candidates and neurotrophic factors have been hypothesized to play a role in the pathogenesis of ADHD. Glial derived neurotrophic factor (GDNF), nerve growth factor (NGF (beta subunit)), and neurotrophic factor 3 (NT3) are members of the neurotrophin family and are involved in the survival, differentiation, and maintenance of neuronal cells. We have examined 10 coding and intronic single nucleotide polymorphisms (SNPs) across GDNF, NGF, and NT3 in a family-based association sample of 120 DSM-IV ADHD probands and their biological parents, as well as a case-control analysis with 120 sex-matched controls. Borderline significant overtransmission of the C allele of a non-synonymous C/T SNP (rs6330) in NGF which codes an alanine/valine change was found in the family-based sample (Chi-square = 3.69, odds ratio (OR) = 1.65, P = 0.05). Although this SNP is located in the 5′ pro-NGF sequence and not the mature NGF protein, it may affect intracellular processing and secretion of NGF. © 2006 Wiley-Liss, Inc.