Hypothyroidism has been frequently reported in systemic sclerosis (SSc), but whether SSc itself increases the risk of thyroid dysfunction is still controversial. The aim of the present study was to determine whether routine thyroid function screening in SSc should be warranted. Serum levels of free triiodothyronine, free thyroxine, and thyroid-stimulating hormone, and the presence of thyroid-specific autoantibodies (antithyroid peroxidase and antithyreoglobulin) were measured in 79 women with SSc and 81 age-matched women with osteoarthritis (OA) serving as controls. Hyperthyroidismwas found in 2 of 79 (2.5%) SSc and in 4 of 81 (5%) OA cases. Hypothyroidism was found in 16 of 79 (20%) patients with SSc (subclinical in 14/16 cases) and in 9 of 81 (11%) patients with OA (subclinical in all cases; P = 0.131). Antithyreoglobulin antibodies were present in 14% versus 13% patients (SSc versus OA, P = NS), whereas antithyroid peroxidase antibodies were present in 23% versus 11% patients (SSc versusOA, P = 0.057). The risk of hypothyroidism was significantly higher in antithyroid peroxidase-positive patients (P < 0.0001), irrespective of the primary diagnosis, and greater in women with OA (OR = 24.6, 95% CI 4.3-141.9, P < 0.0001) than SSc (OR = 4.2, 95% CI 1.2-14.3, P = 0.035). SSc is not independently associated with an increased risk of thyroid dysfunction, but antithyroid peroxidase antibodies may identify a subset of patients at risk of developing thyroid dysfunction.