The degree of tensity of ecological and hygienic state of basic factors can be represented in terms of grades. In St. Petersburg three basic factors reach 5 grades in 7-grade scale. These are radiation, water and atmosphere. By radiation contamination St. Petersburg is on the 5th place after Bryansk, Chelyabinsk, Rostov and Arkhangelsk. As to the number of thyroid diseases, two rises were observed: in the mid 80s and in the mid 90s. A rise in the incidence of thyroid cancer was particularly evident in 1991-1995. The dominating form was papillary carcinoma.