We aimed to investigate the frequency of rheumatic diseases in patients suffering from autoimmune thyroid diseases (ATD). Sixty-five patients (56 F, 9 M), who were followed by diagnosis of ATD, were questioned and examined for the presence of rheumatic disease. Basic laboratory tests and antithyroid antibodies, antinuclear antibody and rheumatoid factor (RF) levels were also measured by appropriate methods. Various rheumatic diseases were detected in 40 (62%) of patients with ATD. The most frequent rheumatic conditions were fibromyalgia, recurrent aphthous stomatitis, osteoarthritis, keratoconjunctivitis sicca and xerostomia and carpal tunnel syndrome which were detected in 20 (31%), 13 (20%), 10 (15%), 9 (14%) and 8 (12%) of patients, respectively. Autoimmune diseases, except Sjogren's syndrome, which were detected in ten patients with ATD, are as follows-vitiligo: two; autoimmune hepatitis: two; oral lichen planus: one, ulcerative colitis: one, inflammatory arthritis in four patients (two of them had rheumatoid arthritis, one had psoriasis and psoriatic arthritis and one had mixed collagen tissue disease). RF was positive in two patients, one of them had rheumatoid arthritis and FANA was positive in six (9%) patients; all of them had hypothyroidism. The frequency of rheumatic diseases seems to be higher in patients suffering from ATD. Initial evaluation and a regular checking for rheumatic diseases in patients suffering from ATD were recommended.