The carpal tunnel syndrome (partial thenar atrophy) is described in 3 patients with acromegaly and in 1 with myxedema. These cases are compared with the more common syndrome of spontaneous partial thenar atrophy. Its principal occurrence in women past the menopause suggests an endocrine rather than a primarily traumatic etiology for most cases with this syndrome. A trial with estrogen therapy is advocated in the early stages.