The total group of hyperkinetic children drawn from the pool of consecutive admissions to a child and adolescent out-patient department were compared with further groups admitted consecutively to the same institution in 1979 and 1980. These other groups consisted of normal controls, conduct disorders, emotional disorders or mixed disorders. The question of validity was studied in terms of several comparisons including sex, age, SES, family history, development characteristics, neurological findings and questionnaire scores. It was found that some data support the concept of concurrent validity of the hyperkinetic syndrome, namely the extremely asymmetric sex distribution in favour of boys, some indicators of developmental delay, the early onset of the symptoms and the higher rates of coordination deficits detected by neurological examination.