OBJECTIVE--To examine any associations between routine ultrasonography in utero and subsequent brain development as indicated by non-right handedness at primary school age and neurological development during childhood. DESIGN--Follow up of 8 and 9 year old children of women who took part in two randomised, controlled trials of routine ultrasonography during pregnancy. SETTING--Clinics of 60 general practitioners in Norway during 1979-81. Maternal and child health centres. SUBJECTS--2161 (89%) of 2428 eligible singletons were followed up, partly through a questionnaire to their parents and partly through information from health centres. MAIN OUTCOME MEASURES--The dominant hand of the child was assessed by 10 questions. Deficits in attention, motor control, and perception were evaluated by five questions. Impaired neurological development during the first year of life was assessed by an abbreviated version of the Denver developmental screening test. RESULTS--The odds of non-right handedness were higher among children who had been screened in utero than among control children (odds ratio 1.32; 95% confidence interval 1.02 to 1.71). No clear differences were found between the groups with regard to deficits in attention, motor control, and perception or neurological development during the first year of life. CONCLUSION--Our data suggest a possible association between routine ultrasonography in utero and subsequent non-right handedness, whereas no association with impaired neurological development was found. As the question on non-right handedness was one of six initial hypotheses, the observed results may be due to chance. None the less, the results suggest that the hypothesis may have some merit and should be tested in future studies.