Autoimmune thyroiditis is often related to non-specific autoimmune organ diseases such as Rheumatoid Arthritis, Sjögren's syndrome, systemic sclerosis, Systemic Lupus Erythematosus or polymyalgia rheumatica. Etiology of autoimmune diseases has not been clearly discovered yet. In many aspects, mechanisms leading to organ-specific autoimmune diseases are identic with mechanisms causing organ-nonspecific autoimmune disease. In many cases genetic disposal combined with specific antigens can be seen. Another possible factor in terms of endogenesis is genus. External factors are important too, such as undergoing infection, stress situations, exposion to ultraviolet radiation. Authors of this work summarize facts about chronic autoimmune thyroiditis and system connective tissue disease. The most literature supports more frequent appearance of these diseases, while the thyroiditis can appear both in clinical form with typical symptoms and in subclinical form.