To meet the diagnostic criteria according to the DSM (Diagnostic and statistical Manual of psychiatric disorders) a couple of aspects have to be considered to meet a diagnosis of adhd:

A. Six (or more) of either 1) Inattention, or 2) Hyperactivity/Impulsivity Symptoms must have persisted for at least 6 months to a degree that is maladaptive and inconsistent with developmental level:

1) Inattention

• often fails to give close attention to details or makes careless mistakes in homework, work, or other activities
• often has difficulties sustaining attention in tasks or play activities
• often does not seem to listen when spoken to directly
• often does not follow through instructions and fails to finish schoolwork, chores, or duties in the workplace (not due to oppositional behavior or failure to understand instructions)
• often has difficulties organizing tasks and activities
• often avoids, dislikes or is reluctant to engage in tasks that require sustained mental efforts
• often loses things necessary for tasks or activities (e.g. toys, school assignments, pencils, books)
• is often easily distracted by extraneous stimuli
• is often forgetful in daily activities

2) Hyperactivity/Impulsivity

Hyperactivity

• often fidgets with hands or feet or squirms in seat
• often leaves seat in classroom or in other situations in which remaining seated is expected
• often runs about or climbs excessively in situations in which it is inappropriate (in adolescents or adults, may be limited to subjective feelings of restlessness)
• often has difficulty playing or engaging in leisure activities quietly
• is often "on the go" or often acts as if "driven by a motor"
• often talks excessively

Impulsivity

• often blurts out answers before questions have been completed
• often has difficulty awaiting turn
• often interrupt or intrudes on others (e.g. butts into conversations or games)

B) Some symptoms causing impairment were present before age 7 More.

C) Some impairment from the symptoms is present in two or more settings (e.g. at school and at home) More.

D) There must be clear evidence of clinically significant impairment in social, academic or occupational functioning More.

E) Occurrence is not exclusively during the course of a Pervasive Developmental Disorder, Schizophrenia or other Psychotic Disorder

The asessment of whether a person has ADHD or not must be done by a psychiatrist who is an expert on ADHD.