Genetic and non-shared environmental factors (factors experienced by one child to the exclusion of his siblings) have been strongly implicated in the aetiology of Attention Deficit Hyperactivity Disorder (ADHD). Shared environmental factors were not implicated. Pregnancy, labour/delivery and neonatal complications (PLDNC) were often associated to ADHD. However, no investigations aimed at delineating the shared/non-shared nature of these factors were reported. In order to identify PLDNC which are more likely to be non-shared, we recruited 65 children with ADHD and assessed their history for PLDNC. 45 of them had non-affected siblings that were also assessed for PLDNC. Compared to their non-affected siblings, ADHD children had significantly higher neonatal complications (p = 0.01). Furthermore, neonatal complications were associated with higher motor activity (p = 0.04) and attention deficits (p = 0.03) in ADHD diagnosed children, suggesting that neonatal complications are more likely to be non-shared environmental factors of etiological relevance to ADHD.