Feline hyperthyroidism is a very common disease of middle-aged and older cats. Hyperthyroidism in cats is caused by an increase in production of thyroid hormones from enlarged thyroid glands, located on both sides in the cat's neck. The average age of cats with hyperthyroidism is 13 years of age; only about 5 percent of hyperthyroid cats are younger than 10 years of age. Wondering if your cat might have hyperthyroidism? Review the most common symptoms of feline hyperthyroidism below, and contact one of our cat thyroid specialists today!