We describe 2 HLA-identical sisters who both received silicone breast implants and subsequently developed polyarticular arthritis and neurologic symptoms. In both patients, HLA typing revealed 3 alleles typically associated with rheumatic diseases: HLA-DRB1*0405 and HLA-DQB1*0302 (associated with RA), and HLA-DRB4*01 (associated with mixed connective tissue disease and autoimmune reactions in patients with silicone breast implants. After removal of the implants, rheumatic as well as neurologic symptoms improved dramatically in both patients. One patient achieved complete remission. The other patient, who initially had more progressive disease, retained mild residual symptoms, but had significant improvement in radiological erosions. We believe that our cases support the theories that silicone may act as a triggering factor in genetically susceptible individuals, and that silicone may represent an adjuvant for the development of autoimmune disease. We discuss the possibility that a manifested spectrum of symptoms after silicone exposure might be more specific for a patient's genetic background than unique for silicone.