Before the introduction of mandatory salt iodination in 1997 the North-Eastern Region of Poland was known to be a moderate iodine deficiency area. Moreover, it was one of the mostly contaminated regions after the Chernobyl accident in 1986. The aim of our study was to evaluate the descriptive epidemiological features of incident thyroid cancers diagnosed among the residents of this area between 1996 and 2005. The Regional Cancer Surveillance Program was used to collect data on 691 newly diagnosed thyroid cancers registered during a 10year period. The average annual incidence of all types of thyroid cancer per 100 000 residents rose from 3.9 in 1996 to 5.5 in 2005 (mean 5.8 cases per 100 000 inhabitants). Thyroid cancer was more frequently diagnosed in women (82%) than in men. The majority of all cases was diagnosed in the age group of 4655 years. There were 12 newly diagnosed cancers in children under 15 years of age (3 cases among children born after the Chernobyl disaster). The commonest histological type was papillary carcinoma (74.5%). Follicular type accounted for 10.9%, oxyphilic 5.4%, medullar - 4.5%, anaplastic - 3.0% and other types for 1.7% of cases. Conclusion: The increased incidence of thyroid cancers between 1996 and 2005 is most likely explained by the improvement in diagnostic techniques, but the effect of ionizing radiation after the Chernobyl accident has also to be taken into account. The influence of iodine deficiency seems to be a less probable factor in view of the predominance of the papillary type of carcinoma.