Several transcranial magnetic stimulation studies have demonstrated that patients with congenital hemiparesis can possess ipsilateral corticospinal pathways projecting from the contralesional hemisphere to the paretic hand. This study reports on signal abnormalities in the pons (focal areas of hyperintensity on T(2)-weighted magnetic resonance imaging), which were observed in the course of the corticospinal tract of the contralesional hemisphere in 6 of 10 patients with evidence for ipsilateral corticospinal projections on transcranial magnetic stimulation, but in none of 13 patients without such projections. Thus this magnetic resonance imaging abnormality seems to be related to the presence of ipsilateral corticospinal projections from the contralesional hemisphere in congenital hemiparesis.