One hundred and forty-one seven-year-old children took part in an extensive neuropsychiatric study. Eight-two of these children had been selected and sampled from a group of 3448 children for whom questionnaires concerning motor control, perception and attention/behaviour had been completed by pre-school teachers. They all showed pre-school signs of both attention deficit and motor/perception dysfunction. The fifty-nine remaining children had been randomly sampled from the group of 3448 children to serve as controls. The study was carried out in a blind fashion. The present paper reports on results of the neuropsychiatric study with special regard to psychiatric disorders in so-called MBD syndromes, defined in accordance with operational criteria. Prevalence figures for marked psychiatric abnormality in MBD were shown to be higher than for psychiatric abnormality in children with 'neuroepileptic' disorders in the Isle of Wight study. Psychotic behaviour was found to be specifically associated with MBD. Hereditary and neuropathogenic factors singly or together possibly caused the 'MBD handicap'. Non-optimal psychosocial factors appear to interact with the MBD syndrome in the moulding of psychiatric disorders.