Thyroid acropachy is an extreme manifestation of autoimmune thyroid disease. It presents with digital clubbing, swelling of digits and toes, and periosteal reaction of extremity bones. It is almost always associated with ophthalmopathy and thyroid dermopathy. During a 26-yr period at our institution, of 178 patients with thyroid dermopathy, 40 had acropachy. Clubbing associated with thyroid dermopathy (pretibial myxedema) was seen in 35 patients. Clubbing usually was not a patient complaint and was noted only by clinical observers. Four of eight patients with hand and extremity radiographs had periosteal reaction. Seven had associated extremity and joint pain; this pain was absent at long-term follow-up. Half of the patients required systemic corticosteroid therapy, 53% required transantral or transfrontal orbital decompression for severe ophthalmopathy, and 18% had the elephantiasic form of dermopathy. Cigarette-smoking rates were 81% for women and 75% for men (mean, 28 pack-years). All 13 patients who had thyroid-stimulating Ig measurement had high titers. Long-term follow-up (median, 12.5 yr) revealed that acropachy was not a complaint in follow-up visits or questionnaires. The data suggest that thyroid acropachy is an indicator of severity of ophthalmopathy and dermopathy. It is a source of clinical concern only if dermopathy is persistent and severe.