The study focuses on individuals who have consecutively presented to participating clinics with suspected attention and/or behavior concerns and would receive a clinician's comprehensive evaluation for ADHD. The study population includes male and female participants aged 6-17.99 years regardless of race, ethnicity, and socioeconomic origin. Because of inclusion of patients with consecutive presentation to provide a representative clinical sample, the exact numbers for sub-groups will not be controlled. The study population will include patients with comorbid conditions. The non-ADHD subgroup will include patients with other causes of attentional concerns, which may include other common psychiatric disorders, organic causes of attention problems (such as poor hearing, vision disturbances, remote head injury, substance abuse), and/or no diagnosis.

Inclusion Criteria:

• Subject willing to voluntarily participate in a research study that includes EEG collection and analysis.
• Family/patient seeking comprehensive clinical evaluation for attention and/or behavior concerns.
• Male or female at least 6 years of age and who will not be over 17.99 years of age upon admission to study.
• Willing to stop any and all current psychiatric medications prior to or by entry into study.
• Subject and parent (or legal representative) of an educational level and degree of understanding sufficient to communicate suitably with the investigator, rater and study coordinator.

Exclusion Criteria:

• Previous diagnosis of mental retardation. IQ < 70 by previous records.
• History of seizure disorder or of EEG abnormalities. On anticonvulsants for seizure control.
• Metal plate or metal device in the head.
• Suicide ideation or gesture and/or homicidal ideation or gesture.
• Concomitant medications during participation in a research study. No prescription or nonprescription medications with psychoactive properties that may affect EEG (such as over-the-counter dietary supplements, pseudoephedrine, or phenylpropanolamine). No antipsychotics, no psychostimulants, no antidepressants. Washout of at least one week or longer depending on the medication and clinician's judgment. Medication used for medical reasons must be cleared by research staff with consideration of known effects on EEG.
• Known serious medical problems (cardiovascular, hematological, liver, seizure disorder, renal, or chronic respiratory problems).