The silicone implant controversy wavers between reassuring epidemiological studies and about 300 case reports of patients developing a definite or incomplete/atypical connective tissue disease (CTD) after receiving a silicone gel-filled breast implant (SBI). Since Hashimoto's thyroiditis (HT) is rarely reported in this context, we report here two new cases of HT associated with a history of bilateral cosmetic SBIs. The first patient was a 45-year-old white woman who had SBIs in 1976. In 1991 she developed HT, evolving to thyroid deficiency which was compensated with levothyroxine treatment. In addition, the patient complained of fatigue, arthralgia, morning stiffness and developed a sicca syndrome necessitating artificial tears. The 1995 evaluation disclosed the presence of antinuclear antibodies at a titre of 1/640, and high level anti-thyroid microsomal antibodies (1/256,000). Gamma globulins rose to 22.6%. Thyroid ultrasonography showed an enlarged thyroid gland with a diffusely hypoechogenic pattern. The implants were painful, and in 1996 they were removed. Microscope examination of the fibrous capsule surrounding the prostheses showed extremely dense connective tissue with fibrosis. The second patient was a 55-year-old white woman who had SBIs in 1984. In 1995, she developed HT with clinical pain and tenderness of the thyroid gland, with mild hyperthyroidism and positive antithyroglobulin antibodies, and was given corticosteroid treatment for 5 months. In 1996, the implants were again painful and the patient developed positive antinuclear antibodies with a titre of 1/200. Ultrasonography showed a heterogeneous thyroid gland, and implant removal was advised. Hashimoto's thyroiditis is recognized as a subset of chronic auto-immune thyroiditis, and its association with SBI is rare. In these 2 observations, an association without relation is possible, but a future survey of similar cases seems warranted.