Cerebellar abiotrophy is a spontaneous, progressive degenerative disease of the cerebellum in which Purkinje cell loss and functional disorders occur secondary to an intrinsic metabolic defect. Clinically, all animals with cerebellar abiotrophy are normal at birth, and neurological signs become evident during development. This work aimed to report and describe a case of cerebellar cortical abiotrophy in an adult American Staffordshire Terrier in Brazil, highlighting the pathologic fi ndings of the cerebellar lesions. Case: A 10-year-old female American Staffordshire Terrier presented with a 3-year history of progressive neurological changes. These changes began with mild ataxia of the hind limbs that involved the forelimbs after 2 years. In the recent months prior to presentation, the patient spent most of her time lying down with a head tilt. When she stood with her head raised, she exhibited abasia and required a broad base of support. When she attempted to walk, she quickly fell and rolled over if not supported. She could not eat on her own because of intense intention tremors. Because of the severity of her condition, the decision was made to euthanize the animal. Necropsy examination revealed no signifi cant fi ndings. Various organ specimens were collected, fi xed in 10% formalin, and processed for routine histology. The tissue sections were stained with hematoxylin and eosin. Cerebellar specimens were subjected to immunohistochemistry (IHC). Two cerebellar specimens from two normal 8- to 9-year-old American Staffordshire Terriers were used as positive controls for IHC and comparative evaluation of the lesions. Histologically, the main changes were observed in the cerebellum and were characterized by necrosis, degeneration, and marked segmental loss of Purkinje cells; moderate reduction in the granular cells of the cerebellar cortex; and thinning of the molecular layer. Cerebellar IHC in the affected canine showed a slight reduction in immunoreactivity for neurofi laments in both the molecular layer and white matter as well as a marked increase in immunostaining for glial fi brillary acidic protein, indicating astrogliosis, in the molecular layer, granular layer, and white matter. Discussion: The diagnosis of cerebellar abiotrophy in this canine patient was based on clinical, pathologic, and immunohistochemical fi ndings. The framework cerebellar syndrome in an adult dog, slowly progressive, as in this case (10 years old with a 3-year clinical progression) is compatible with abiotrophy in the American Staffordshire Terrier. The main gross lesions observed in the cerebellum of canines with abiotrophy are projected to decline; however, these changes can be subtle, as in this case. Histopathology revealed a primary loss of Purkinje cells and depletion of the molecular and granular layers. These characteristics have been identifi ed as hereditary in American Staffordshire Terriers and other breeds. The clinical signs observed in this patient, namely ataxia, intention tremors, and abasia, refl ect the loss of function of the inhibitory neurons of the cerebellar cortex. The fact that cerebellar abiotrophy is relatively common in purebred dogs and the great variety in the early clinical signs and progression suggests different genetic etiologies in different breeds. An association with breed is evidenced by the fact that the clinical manifestations of cerebellar abiotrophy in American Staffordshire Terriers start late and have been shown to be hereditary. This paper reports the occurrence of cerebellar cortex abiotrophy as a cause of neurological disease in an American Staffordshire Terrier in Brazil.