Thyroid associated ophthalmopathy (TAO) is an inflammatory orbital disease of autoimmune origin with the potential to cause severe functional and psychosocial effects. It presents one of the most difficult challenges in the clinical practice of ophthalmology. Pathogenesis of the disease is not yet fully understood. It is usually associated with thyroid dysfunction. TAO has a variable clinical presentation; it may cause severe damage to vision and orbital architecture. TAO is the most frequent cause of unilateral or bilateral proptosis in adults. Potential sight-threatening complications include optic neuropathy and severe corneal exposure keratopathy. Most patients do not require specific therapy. Those with moderately severe or severe disease are treated with steroids and/or orbital radiation during the inflammatory phase and surgical therapy during the inactive phase. Decompression may be needed in either phase. Although appropriate treatment can restore near normal function and appearance in most cases, the management of TAO is difficult, controversial, and far from optimal. Disease severity is the key determinant of the indication for therapy, while therapeutic choice depends on inflammatory activity. Clinical management is difficult because no immediate or dramatic cure exists. With appropriate medical and surgical treatment, patients can be restored to normal function and appearance in most cases, but the process to reach this goal will usually be lengthy.