A 52 year-old female with no significant medical problems presented with left-sided weakness, unsteady gait and speech disturbance. It was thought that she had neuro-inflammation and she remained clinically stable. Several years later, she was diagnosed with latent autoimmune diabetes of adulthood. Her neurological symptoms deteriorated and she was admitted into hospital. The cerebrospinal fluid was normal, as were an array of blood tests. Imaging tests, including magnetic resonance imaging, computerised tomography and positron emission tomography scans were normal. However, her anti-glutamic acid decarboxylase antibody serum level, which had been taken in the diabetes outpatient clinic, returned at 2,000,000 IU/mL (normal range 0–10). This led to the diagnosis of glutamic acid decarboxylase (GAD) positive cerebellar ataxia. She was treated with plasma exchange and intravenous immunoglobulins and over next 12 weeks her symptoms improved. Our case highlights the need for appropriate treatment of patients with GAD positive cerebellar ataxia to achieve good outcomes.