Delirium is common in older people. It is a crucial diagnosis because it raises the morbidity and the mortality. Diagnostic tools like Mini Mental State Examination (MMSE), the confusion assessment method (CAM), and the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSMIV), can help with the diagnosis. We report a case of a woman with neurological symptoms which look like dementia. We diagnosed systemic lupus erythematosus (SLE). The apparition of late-onset SLE is more insidious, which leads to misdiagnosis. We will discuss about the difficulty of the differential diagnosis between delirium, depression and dementia in our patient and the difficulty to manage treatment of neurolupus in older people.