A twenty-month-old Chihuahua male dog was presented to us suffering with ataxia. Based on the physical examination, X-ray and magnetic resonance imaging (MRI) examinations, we diagnosed the dog with hydrocephalus, Chiari I malformation and syringomyelia. Treatment consisted of internal medical treatment and the placement of a ventriculoperitoneal (VP) shunt. The ventricular dilatation was relieved and the dog improved neurologically; however, the Chiari I malformation and syringomyelia remained after surgically positioning the VP shunt.