The authors report eleven cases of multiple auto-immune syndrome, concerning a total of 15 different auto-immune diseases. This study suggests that auto-immune thyroid disorders (Graves' disease or hypothyroidism resulting from Hashimoto's thyroiditis) are a common feature of multiple auto-immune syndromes, while antithyroid antibodies are constant among our patients. Sjögren's syndrome is also very prevalent, and seems to be non-randomly associated with auto-immune thyroid disorders, a fact which suggests common aetiological factors. Among other auto-immune disorders, the antiphospholipid syndrome has been diagnosed twice. A genetic predisposition to multiple auto-immune syndrome is obvious, as shown by a familial history of auto-immune disorders (found in more than half of the cases), and a predominant HLA phenotype, B8 and/or DR3. The authors plead for a systematic enquiry for multiple auto-immune syndrome in patients with auto-immune thyroid disorders and a family history of auto-immune disorders.