The authors review the most common situation concerning oncological patients with concomitant thyroid disease. In case of unknown origin of metastasis and nodular goitre the ultrasound examination with fine needle aspiration biopsy confirms or excludes the thyroid origin. The euthyroid sick syndrome is often diagnosed in oncological patient as a consequence of oncological disease and it doesn’t mean hypothyroidism. If oncological patients prove to have a thyroid functional failure the endocrinologist must correct the function as fast as possible to enable oncological treatment. There is no evidence that chemotherapy can influence the thyroid function, but radiotherapy can cause thyroiditis with later hypofunction. The interferon therapy causes thyroid dysfunction in l0% of patients and the recommendation to examine not only TSH and FT4 but also thyroid antibodies is warranted. Lymphoma of the thyroid gland occurs most often on the basis of lymphocytic thyroiditis and lymphocytic thyroiditis may be a risk factor for papillary carcinoma of the thyroid as well. Women with breast carcinoma were proved to have lymphocytic thyroiditis with minor thyroid hypofunction more often than the corresponding group of women with colon cancer or control group of healthy women. In case of renal tumor (Grawitz), breast or lung carcinoma the thyroid can be attacked with metastasis, and ultrasound with fine needle biopsy can reliably differentiate between primary or secondary thyroid involvements. The thyroid can be involved in some diseases: multiple endocrine neoplasia, Carney, Cowden and Gardner’s syndromes.

        Key words: thyroid, hypothyroidism, hyperthyroidism, breast carcinoma, lymphoma, cytokins.