Turner's syndrome (TS) is characterized by short stature and gonadal dysgenesis. It is often associated with systemic manifestations, such as cardiovascular, gastrointestinal, and musculoskeletal disorders. Although very rare, it is possible for TS to accompany autoimmune disease, including thyroid disease, inflammatory bowel diseases, diabetes mellitus, psoriatic arthritis, and juvenile rheumatoid arthritis. A 39-year-old woman was referred for symmetric polyarthritis of her hands and feet. She had been diagnosed with Turner's syndrome with 46,XO,-X,+fragment before the age of 22 years and had developed autoimmune hypothyroidism treated with thyroid hormone replacement. At the time of first visit, she had polyarthralgia with morning stiffness for more than 3 months. The musculoskeletal examination revealed symmetrical polyarthritis affecting the metacarpophalangeal, proximal interphalangeal, and metatarsophalangeal joints, fulfilling the ACR 1987 revised criteria for rheumatoid arthritis (RA). Here, we present an unusual case of RA associated with TS. It is important to pay meticulous attention to patients with TS so that inflammatory arthritis is not neglected and the diagnosis is not delayed.