Symptoms of childhood attention-deficit/hyperactivity disorder affect cognitive, academic, behavioral, emotional, social, and developmental functioning. Attention-deficit/hyperactivity disorder is the most commonly diagnosed neurodevelopmental disorder in children and adolescents. An estimated 2 to 16 percent of school-aged children have been diagnosed with the disorder. The prevalence of attention-deficit/hyperactivity disorder in the primary care setting is similar to that in the general community, depending on the diagnostic criteria and population studied. The causality of attention-deficit/hyperactivity disorder is relatively unknown. Most recent studies focus on the role of dopamine; norepinephrine; and, most recently, serotonin neurotransmitters. The disorder is classified into three general subtypes: predominantly hyperactive-impulsive, predominantly inattentive, and combined. Screening tools and rating scales have been devised to assist with the diagnosis. Appropriate treatment can dramatically improve the function and quality of life of the patient and family. Pharmacologic treatment includes stimulants, such as methylphenidate and mixed amphetamine salts, or nonstimulants, such as atomoxetine. Behavioral approaches, particularly those that reward desirable behavior, are also effective. A combination of pharmacologic and behavioral therapies is recommended.