Hypereosiophilia-induced encephalopathy (HE) is a rare but well-described clinical syndrome. However, serial magnetic resonance imaging (MRI) findings of HE have rarely been reported. We describe serial MRI findings of three patients with HE. The patients presented with acute confusion, focal neurological deficits and/or seizures. Eosinophils in repeated blood tests were more than 3000/mm3 in all the patients. Echocardiography in two patients showed findings consistent with eosinophilic endomyocardial fibrosis or global hypokinesia. The initial MRI revealed multiple high-signal lesions on T2-weighted images with gadolinium-DTPA enhancement on T1-weighted images, which were predominantly distributed in the border zone of the middle-anterior cerebral arteries and the middle-posterior cerebral arteries. The second MRIs taken prior to the initiation of steroid therapy showed that the lesions increased in size and number in the same area. The third MRIs performed long after the therapy showed that the lesions were shrunken. A brain biopsy specimen in one patient showed reactive gliosis following infarction with abundant intravascular eosinophils. The MRI-identified lesions in the patients with HE thus develop mainly in the border zone. The lesions occasionally increase in size and number and shrink if the eosinophilia is adequately treated. Although the nature of the MRI-identified lesions remains unclear, their pathogenesis may be related to multiple embolisms associated with concomitant cardiac abnormality and hypercoagulable state.