BACKGROUND: Giant cell arteritis (GCA) is a vasculitis primarily affecting medium- and large-sized arteries. The diagnosis may be challenging and lead to delays in treatment. Cerebrospinal fluid (CSF) pleocytosis is an uncommon association but may occur due to central nervous system (CNS) vasculitis or pachymeningitis. We describe a case fulfilling the criteria for diagnosing GCA, associated with CSF pleocytosis and normal neuroimaging. CASE PRESENTATION: A 76-year-old woman presented to our regional hospital with three weeks of fever, confusion and fatigue. Two days later, she developed a right temporal headache with scalp tenderness. Preliminary investigations, including an FDG-PET scan, were unrevealing. Cerebrospinal fluid sampling demonstrated an isolated mononuclear pleocytosis. Brain magnetic resonance imaging (MRI) and an extensive panel of investigations failed to identify a cause, and a diagnosis of aseptic meningitis was made. An ultrasound of her right temporal artery was performed which demonstrated a non-compressible halo sign consistent with GCA. The patient was commenced on high-dose corticosteroid therapy with significant improvement in her symptoms. CONCLUSIONS: This case strengthens the association of CSF pleocytosis occurring as a complication of GCA and alerts clinicians to consider the possibility of GCA as a potential aetiology for aseptic meningitis.