Sweet disease, also known as acute febrile neutrophilic dermatosis, is an idiopathic multisystem inflammatory disorder characterised by erythematous skin lesions and fever. "Neuro-Sweet disease" is a rare central nervous system involvement that coexists with the characteristic cutaneous lesions of Sweet disease. Here, we report a case of Sweet disease complicated with acute encephalopathy. This case showed extensive lesions in the cerebral white matter on magnetic resonance imaging (MRI) and high protein concentration in the cerebrospinal fluid (CSF) without pleocytosis. After steroid therapy, the patient's clinical syndrome recovered completely with no significant neurological deficits or abnormal findings on brain MRI, and normalization of the high CSF protein concentration. Both clinical and MRI findings suggested that the marked leukoencephalopathy in this case was mainly due to reversible oedema rather than destructive structural alterations in the cerebral parenchyma.