The aim of the study was to assess whether radioactive fallout from the Chernobyl accident in 1986 influenced thyroid cancer incidence among children and adolescents in Finland. The population was divided into two: those with thyroid doses less than 0 6 mSv and above 0.6 mSv. Cumulative incidence of thyroid cancer was identified from the Finnish Cancer Registry from a population aged 0-20 years in 1986 with a total of 1,356,801 persons. No clear difference in underlying thyroid cancer incidences rates were found during the pre-Chernobyl period (1970-1985) (rate ratio RR 0.95, 95% confidence interval CI 0.81-1.10). During the post-Chernobyl period (1991-2003), thyroid cancer incidence was lower in the more exposed population than in the less exposed population (RR 0.76, 95% CI 0.59-0.98). Our results did not indicate any increase in thyroid cancer incidence related to exposure to radiation from the Chernobyl accident.