A 3-year-old girl with left hemiparesis suffered from bilateral paresis, motor rigidity, gait disturbance, axial hypotonia, dysarthria, apathy, and incontinence. After steroid therapy, mild improvement occurred, but muscle weakness, gait disturbance, and rigidity remained. Leigh encephalopathy was excluded on the basis of muscle biopsy and laboratory findings. Computed tomography and serial magnetic resonance imaging at an early stage revealed right-sided dominant lesions in the putamen and caudate nucleus and later bilateral striatal lesions, appearing as hyperintense signals on T2-weighted images and mixtures of hypo- and hyperintense signals on T1-weighted images. This is the first demonstration of serial magnetic resonance imaging findings in infantile bilateral striatal necrosis.