Tehran University of Medical Sciences Iranian Journal of Psychiatry 1735-4587 7 3 2012 09 15 109 13 Ahmad Ghanizadeh Research Center for Psychiatry and Behavioral Sciences, 2Department of Psychiatry, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran. Marzie Abotorabi-Zarchi Mohammad Reza Mohammadi Ali Firoozabadi Research Center for Psychiatry and Behavioral Sciences, Department of Psychiatry, Hafez Hospital, Shiraz, Iran 2015 10 14 Objective: It is not clear whether sibling’s gender ratio is associated with attention deficit hyperactivity disorder (ADHD). This study examines whether inattentiveness severity and hyperactivity/impulsivity severity are associated with birth order of children with ADHD. Method: Participants are a clinical sample of 173 children and adolescents with ADHD and 43 ones without ADHD. Diagnoses were made using Diagnostic and Statistical Manual of Mental Disorders forth edition-Text Revision (DSM-IV-TR), diagnostic criteria according to faceto-face interview with the children and their parents. ADHD DSM-IV checklist was used to measure inattentiveness and hyperactivity/impulsivity scores . Results: The association of birth order and diagnosis of ADHD was not statistically significant after adjusting for covariate factors. The gender ratio of siblings is not associated with ADHD. Conclusion: Birth order and siblings gender ratio are independent of ADHD diagnosis. The results of this study support the fact that genetic factors rather than environmental factor of birth order is associated with ADHD. Moreover, contrary to autism, the current results do not suggest the androgen theory for ADHD. https://ijps.tums.ac.ir/index.php/ijps/article/view/240 https://ijps.tums.ac.ir/index.php/ijps/article/download/240/236