The cardinal symptoms of attention-deficit/hyperactivity disorder (ADHD) are inattention, hyperactivity and impulsivity. Etiologically, ADHD is mainly put down to genetic causes; it entails a considerable range of psychosocial problems for those affected and their social environment. The parents of a total of 7,569 boys (B) and 7,267 girls (G) aged 3-17 who took part in the German Health Interview and Examination Survey for Children and Adolescents (KiGGS) answered a self-administered questionnaire including an ADHD diagnosis question and the Strengths and Difficulties Questionnaire (SDQ). In addition behavioural observations of 7,919 children (aged 3-11) were carried out during the medical and physical tests. Participants whose parents reported that they had ever been given an ADHD diagnosis by a doctor or psychologist were classified as ADHD cases. Participants were classified as suspected cases of ADHD if they had a value of > or =7 on the SDQ inattention/hyperactivity scale. ADHD had ever been diagnosed in 4.8 % of the children and adolescents altogether (B: 7.7 %, G: 1.8 %). Another 4.9 % of the participants can be considered as suspected cases. Already 1.8 % of the preschoolers had been given an ADHD diagnosis. At primary school age (7-10 years old) the frequency of diagnosis rises sharply. At age 11-17, ADHD had ever been diagnosed in 1 in 10 boys and 1 in 43 girls. ADHD had been diagnosed significantly more frequently among participants of low socio-economic status (SES) than among participants of high SES. A diagnosis of ADHD is reported less often for migrants, they rank more frequently among the suspected cases. The discrepancy between confirmed and suspected cases of ADHD among migrants may point to lower diagnosis rates or lower utilization of medical services. The short- and long-term medical, social and health-economic effects of ADHD illustrate the major public health relevance of the disorder. As for prevention, the high share of genetic factors in ADHD etiology primarily suggests secondary prevention (early support and early diagnosis) and tertiary prevention measures. Further analysis of the KiGGS data could prospectively identify risk groups more precisely and refine preventional approaches.