We report the case of a 56-year-old woman treated with aromatase inhibitors for a breast cancer. Following one year of such therapy, the patient presented with widespread osteoarthrealgia. The clinical picture worsened 3 years later when the pain became more severe with swelling and stiffness involving several joints in a symmetric fashion. Biochemical analysis showed an increase of ESR, CRP and rheumatoid factor, as well as of anti-CCP antibodies. The x-ray was compatible with a diagnosis of rheumatoid arthritis (RA). Therapy with methotrexate, prednisol one, bisphosphonates and vitamin D was started, achieving a quick clinical remission. Aromatase inhibitors have been shown to alter the distribution of Th1/Th2 lymphocytes and increase the level of RANKL. A possible role of aromatase inhibitors in RA development has been further addressed.