OBJECTIVES: To establish the role of clinical and laboratory investigation of the cardiovascular system in children with Down's syndrome. DESIGN: Prospective evaluation; examiners blinded to results of laboratory studies. SETTING: Tertiary pediatric referral centre. PATIENTS: Fifty consecutive children with Down's syndrome presenting to a regional genetic centre. Children less than six weeks of age or with known heart disease were excluded. MEASURES: Following independent examinations by a geneticist and a pediatric cardiologist, an electrocardiogram (ECG) and two-dimensional and Doppler echocardiograms were carried out. RESULTS: Assessment by the geneticist yielded two false positives and five false negatives (sensitivity 67%, specificity 88%). Addition of an ECG to clinical evaluation increased the sensitivity to 80% and specificity to 90%, a rate comparable with clinical assessment by a cardiologist. No lesion requiring surgical correction was missed by this combination. CONCLUSIONS: Where expertise in pediatric echocardiography is not readily available, careful clinical assessment coupled with the interpretation of an ECG is adequate and appropriate screening of the child with Down's syndrome.