Rheumatoid leptomeningitis is a rare complication of rheumatoid arthritis (RA). We describe a woman with rheumatoid leptomeningitis presenting with acute-onset behavioral changes and consciousness disturbance in the early stage of RA. On fluid-attenuated inversion recovery images or diffusion-weighted images, high-signal-intensity lesions in the subarachnoid spaces of the right frontal lobe were observed. Biopsies of brain tissues and the dura mater located in the right frontal lobe were obtained. On the basis of the findings of histopathological analysis, a diagnosis of necrotizing granulomas involving the leptomeninges consistent with rheumatoid leptomeningitis was made. An early diagnosis of rheumatoid leptomeningitis and immediate initiation of treatment may prevent neurological sequelae.