Vitamin B₁₂ deficiency can cause subacute combined degeneration of the spinal cord and cerebellar lesions. The patient, a 78-year-old woman, presented with an unstable gait, speech impairment and memory decline for one month. The neurological examination revealed ataxia, cerebellar speech disorder and mild cognitive impairment. Head and cervical vertebra magnetic resonance imaging (MRI) showed spinal cord and cerebellar lesions. The patient’s symptoms improved after supplementation with vitamin B₁₂. We found few reports of such cases in the literature. In this case report, we describe the entire diagnostic and treatment process of vitamin B₁₂ deficiency involving cerebellar lesions and briefly discuss the related pathogenesis, research progress and treatment.