Objectives: This research was to determine the pattern of psychiatric disorders in the immediate family members of children with attention deficit hyperactivity disorder (ADHD). Family genetic risk factors were also evaluated. Method: 227 immediate family members, 120 parents and 107 siblings of 60 ADHD children and adolescents between the ages of 5 to 17 years were evaluated. Psychiatric clinical interviews, K-SADS, SADS, and Wender determined ADHD and family members’ diagnosis. Evaluation of presence of ADHD diagnosis and other psychiatric diagnosis were based on DSM-IV standards. Findings: The most prevalent psychiatric diagnosis in the families was disorders of depression (51.7%), ADHD (48.3%), anxiety (41.7%), and obsessive compulsive (25%). The most prevalent diagnosis, comorbid to ADHD was disorders of Enuresis (38.3%), obsessive-compulsive (31.7%), anxiety (30%), and tic (26.7%); in the adolescent group, it was bipolar disorder with 37.5%. Results: The high prevalence of ADHD in the afflicted families indicates strong influence of genetic factors. The presence of comorbid disorders to ADHD and high prevalence of affective and anxiety disorders in the families of ADHD may point to homogeneity in genetic etiology in these disorders and subgroups of ADHD whose risk factors, etiology, and treatment responses may differ.