The study analyzes the prevalence of thyroid disease in 1960 healthcare workers, classified as occupationally exposed to ionizing radiation, who have worked at the University Hospital of Pisa. They underwent a medical surveillance protocol from January 2005 until Mars 2012 at the Operative Unit of Occupational Medicine. A positive history of thyroid disease was found in 221 persons, but only 110 (the 5.61% of the population) developed the disease during or after the occupational exposure. Benign thyroid diseases, found in 93 workers, were in order of frequency: Hashimoto's thyroiditis, nodular disease, Basedow's disease, multinodular goiter, subacute thyroiditis and hypothyroidism. Malignant thyroid diseases were found in 17 workers (the 0.87% of the total population), 15 workers suffered from the papillary histotype and 2 from the medullary histotype.