Neurologic complications of allogeneic hematopoietic cell transplantation (allo-HCT) include infections, cerebrovascular events, therapy-induced neurotoxicity, recurrent malignancies, and neurologic manifestations of graft-versus-host disease (GVHD). Anti-glutamic acid decarboxylase (GAD) antibody-associated cerebellar ataxia is a well-established disorder of autoimmune origin, but there are no reports in the literature of its occurrence following allo-HCT. We describe a middle-aged woman with chronic GVHD after allo-HCT who presented with a rapidly progressive cerebellar syndrome. Thorough investigation revealed only cerebellar atrophy on brain imaging and positive anti-GAD65 antibodies in serum and cerebrospinal fluid suggesting the diagnosis of anti-GAD antibody-associated cerebellar ataxia. Despite prompt treatment with high-dose corticosteroids, intravenous immunoglobulins, and rituximab, the patient’s condition rapidly deteriorated, and she died 4 months later. This case suggests that anti-GAD antibody-associated cerebellar ataxia may be a rare manifestation of chronic GVHD.