An 11 year old, indoor/outdoor, spayed female domestic shorthair feline, presented to the Cornell Internal Medicine Service for fever, weight loss, lethargy, and inappetence of a two week history. She had been initially treated by the referring veterinarian with antibiotics and steroids, however, no clinical improvement was reported. Physical examination showed mild dehydration, fever, and chorioretinitis. Blood results showed a non-regenerative anemia. An FeLV/FIV SNAP test was negative. Systemic hypertension was ruled out. A Cryptococcus titer was negative and Toxoplasma titer was pending. She was treated on a presumptive diagnosis of Toxoplasma gondii, later confirmed by serology. Follow up with the owner showed that the cat had made a full recovery. The diagnostic approach to a fever of unknown origin and pathology of Toxoplasma gondii infection are discussed.