"Maggie", a four year old female spayed Dutch Smoushund, presented to the Cornell University Hospital for Animals for evaluation of a progressive encephalopathy of six months duration that failed to respond to medical management with steroids. Other chronic progressive abnormalities included decreased vision and bradycardia. Initial diagnostics included a complete blood count, a chemistry panel, a urine analysis, thoracic radiographs and abdominal ultrasound, the results for which revealed no significant abnormalities. A fundic exam revealed decreased retinal vasculature in the left eye and infiltrative lesions of the fundus of both eyes. A subsequent ocular ultrasound showed retinal detachment in the left eye. An MRI showed a focal area of hyperattenuation on the right side of the cerebrum with regional cerebral edema and cerebellar herniation. Cytologic analysis of a sample of the cerebral spinal fluid was suggestive of lymphoma. Based on these findings, a presumptive diagnosis of lymphoma originating within the central nervous system with probable extension along the optic nerve into the eyes was made. Due to the poor prognosis and progressive decline in Maggie's condition, Maggie was humanely euthanized. Necropsy allowed for the definitive diagnosis of a primary T-cell lymphoma of the central nervous system.