Biological Markers in Attention Deficit/Hyperactivity Disorder (ADHD)

* INCLUSION REQUIREMENTS-PROBANDS: Current age of index probands: 15.21 plus or minus 3.42; previous participation in the NIMH Child Psychiatry Branch ADHD study. Age adjusted dimensional ratings (Conners Rating Scales-Revised, and Strengths and Weaknesses of ADHD and Normal Behavior (SWAN)) of hyperactivity/impulsivity greater than or equal to 95th percentile for index and second sibling. Primary ratings for the index proband will be provided by main teacher. Up to 150 ADHD probands for reassessment. Consent and assent obtained in writing. EXCLUSION CRITERIA - PROBANDS: Presence of other known genetic conditions that are likely to be etiologic. Onset of medical conditions that could produce symptoms of ADHD through non-genetic mechanisms (e.g., thyroid disorders, seizure disorders, inborn errors of metabolism, extremely low birth weight (less than 1000 gm), meningitis, intracranial pathology). Presence of other psychiatric disorders that can produce symptoms similar to ADHD (e.g., major depression, bipolar disorder, severe anxiety disorders, pervasive developmental disorders, psychotic disorders, post-traumatic stress disorder). Presence of neuropsychiatric conditions that may confound evaluation of ADHD (e.g., Tourette's syndrome, obsessive-compulsive disorder, or PANDAS (pediatric autoimmune neuropsychiatric disorders associated with streptococcus), intelligence quotient less than 80, reading achievement standard scores less than 75 or reading-intelligence discrepancy greater than 2 SD). INCLUSION REQUIRMENTS-RELATIVES: Subjects must be relatives of probands. Consent and assent obtained in writing. INCLUSION REQUIREMENTS -NORMAL VOLUNTEERS: Up to 150 newly accrued normal volunteers unrelated to probands. Same age range as probands. Parent and teacher ratings within one SD of population means on ADHD/hyperactivity factors. Consent and assent obtained in writing. EXCLUSIONS - NORMAL VOLUNTEERS: Presence of ADHD. Presence of any other psychiatric disorders on structured psychiatric interview (DICA-IV). Presence of known genetic conditions. Onset, presence or history of medical conditions that could produce symptoms of ADHD through non-genetic mechanisms (e.g., thyroid disorders, seizure disorders, inborn errors of metabolism, extremely low birth weight (less than 1000 gm), meningitis, intracranial pathology).