A 19-yr-old female lynx (Lynx canadensis) presented for an acute onset of anorexia and reluctance to move. Physical examination, radiography, hematology, and serum biochemistry revealed evidence of renal failure, presumptive uremic gastritis, chronic intervertebral disk disease at T13-L1, and markedly low serum levels of total thyroxine (1.54 nmol/L) and total triixodothyronine (0.55 nmol/L). Twenty-five hours after its original presentation, the lynx exhibited horizontal nystagmus, which has been suggested as a clinical sign associated with hypothyroidism in domestic dogs. The lynx was euthanatized because of poor prognosis, and medical management concerns related to its chronic renal failure. Necropsy examination substantiated that the lynx had true hypothyroidism with 60-90% of the thyroid gland replaced with adipose tissue. Although feline adult-onset hypothyroidism may have low incidence, it should still be considered as a cause of nonspecific signs of disease in cats, as well as signs suggestive of hypothyroidism. Routine monitoring of baseline exotic felid thyroid levels throughout life would help to identify normal values and diagnose a potential disease that has obscure clinical signs.