Severe cerebral and systemic necrotizing vasculitis developing during pregnancy in a case of systemic lupus erythematosus. We describe a fatal case of systemic lupus erythematosus (SLE) developing cerebral and systemic necrotizing vasculitis during pregnancy. The patient was discovered to have SLE at 14 weeks' gestation. Although the symptoms disappeared without treatment with corticosteroid in the 2nd trimester, she presented with meningoencephalitis due to vasculitis in the 3rd trimester. Polyarteritis nodosa (PAN)-like necrotizing vasculitis of the small muscular arteries and arterioles, with acute and healing lesions in the leptomeninges, brain parenchyma and visceral organs was observed at postpartum autopsy. PAN-like vasculitis in the central nervous system is quite rare in SLE. This case is also suggestive in terms of the influence of pregnancy on the activity of SLE. 