Cerebral infarction occurs in about 1% of patients with cyanotic congenital heart diseases such as tetralogy of Fallot and transposition of great arteries, the majority of the patients being under 2 years of age. In this study, brain ultrasonograms of 8 month-old infant with tetralogy of Fallot, polycythemia and iron deficiency (RBC 736×104 /mm3, Fe 41 μg/dl) since the onset of illness, which occured as right side hemiplegia, were studied serially. Homogeneously hyperechoic lesion of left caudate nucleus, putamen and internal capsule and narrowed anterior horn of left lateral ventricle were apparent on the day of onset. At 1∼2 weeks later, echogenicity of the lesion became intenser than it had been at the onset and gradually weakened thereafter. On the other hand, the lesion was presented as low density area on CT images since the onset. These CT findings and serial changes in echogenicity since onset would seem to indicate that the lesion was a nonhemorrhagic infarction.