Introduction:Attention-deficit/hyperactivity disorder (ADHD) is defined as a behavioral disorder with onset in childhood (at the age of 7 years) characterized by symptoms of inattention and impulsivity. hyperactivity. Based on the type of predominant symptoms, ADHD is classified as follows: Combined type: both inattention and hyperactivity/impulsivity symptoms are present Predominantly inattention subtype Predominantly hyperactive/impulsive subtype Not otherwise specified (NOS): people with an atypical disorder with characteristics Sex/age ratio: • ADHD is a developmental disorder that requires the appearance of symptoms before the age of 7. After childhood, symptoms may persist into adolescence and adulthood, or improve or disappear. • The percentages in each group are not well established, but it is estimated that at least 15-20% of children with ADHD maintain the full diagnosis into adulthood. Up to 65% of these children will have ADHD or some residual ADHD symptoms as adults. • The prevalence rate among adults has been estimated between 2 and 7%. The prevalence rate of ADHD in the general adult population is 4 to 5%. • In children, ADHD is 3 to 5 times more common in boys than in girls. Some studies report an incidence rate as high as 5:1. The predominantly inattentive type of ADHD is more common in girls than in boys.• In adults, the sex ratio is closer to equality.Epidemiology: Incidence in school-aged children is estimated between 3 and 7%. The prevalence of ADHD varies by race and ethnicity, with Mexican children having a consistently lower prevalence compared to other racial or ethnic groups. The prevalence of ADHD increases up to 10% for children whose family income is less than 100% of the poverty level and 11% for those whose family income is 100-199% of the poverty level..Causes: As such, no single etiology has been identified for ADHD. ADHD is a heterogeneous disorder that currently results from a complex interaction between psychosocial stressors, environmental factors, neurochemical/neuro-anatomical factors, familial and genetic factors. comorbidity related to levels of stress and psychosocial adversity• Higher levels of stress and psychosocial adversity in children with ADHD and comorbid anxiety or mood disorders than in children with ADHD alone. • Children with ADHD and no comorbidities had levels of psychosocial stress no different from controls.Environmental factorsComplications of pregnancy and childbirthThese factors include: • Prenatal and childbirth complications • Prenatal or perinatal brain injury • Prematurity • Small for gestational age • Low birth weight The following factors have not been supported by research as being associated with the development of ADHD. .• Allergic or toxic reactions to food additives• Refined sugarEnvironmental factorsOthers:• Exposure to toxins• Mercury, manganese, lead• Polychlorinated biphenyls