We performed positron emission tomography (PET) using 18F-labeled 2-F-2-deoxyglucose in 13 patients with systemic lupus erythematosus (SLE). Ten of them had clinical signs of central nervous system involvement (NP-SLE). All patients with neurologic symptoms showed pathologic changes on PET, always in accordance with the clinical state. Three patients without neuropsychiatric manifestations had normal PETs. Computed tomography of the brain and magnetic resonance imaging proved to be less sensitive to both presence and localization of CNS lesions. We conclude that the combination of PET and MRI constitutes the most useful diagnostic procedure for NP-SLE.