We report a case of central nervous system (CNS) lupus showing peculiar findings on cranial magnetic resonance imaging (MRI) with remarkable improvement after corticosteriod therapy. The patient was a 28-year-old woman, admitted to our hospital with severe fever, general malaise, and facial edema on June 4, 2001. After admission, she was diagnosed with systemic lupus erythematosus (SLE). On June 6, she showed diplopia at a distance, and on June 10, she suddenly became unconscious and developed general convulsions. Cranial MRI showed asymmetrical, multifocal, high signal intensity lesions on T2-weighted image (T2-WI) and low signal intensity on T1-weighted image (T1-WI). These lesions were primarily present in the subcortical white matter, with some detected in the overlying cerebral cortex. Gadolinium (Gd)-DTPA enhanced T1-WI showed marked leptomeningeal enhancement overlying the lesions on T1-WI and T2-WI. Apparent diffusion coefficient image (ADCI) showed high signal intensity in the surrounding areas of the T1-WI and T2-WI lesions, and low signal intensity in the central areas of the lesions. Diffusion weighted image (DWI) showed high signal intensity in the central areas of the low signal intensity on ADCI. Cerebrospinal fluid (CSF) examination revealed albuminocytologic dissociation (cell counts of 2/microliter and protein level of 108 mg/dl). CSF IgG index was elevated to 1.152 (normal < 0.7) and interleukin-6 (IL-6) activity to 27.2 pg/ml (normal < 4.0). On June 10, Intravenous administration of high-dose methylprednisolone (1,000 mg/day for 3 days) was started to treat CNS lesions of SLE. Her CNS manifestations, CSF findings, and the lesions on the cranial MRI improved remarkably. This is the first case report describing the lesions on both ADCI and DWI in a case of CNS lupus. The findings of ADCI and DWI suggest that the lesions of high signal intensity on ADCI indicate interstitial edema caused by inflammatory microangiopathy, and the lesions of high signal intensity on DWI and low signal intensity on ADCI indicate cytotoxic edema caused by ischemic change resembling microinfarction. We speculate that in addition to usual T1-WI and T2-WI, performing ADCI and DWI is useful for understanding the pathogenesis of CNS lupus lesions, and may play a significant role in the prognosis.