Health checks of more than 300,000 children from areas around the Fukushima nuclear plant have begun in Japan.
They will have follow-up exams every two years until they turn 20.
Residents have expressed concern about possible thyroid disorders because of exposure to radiation, that has been leaking from the plant since the earthquake and tsunami on 11 March.
Until now, screening has focussed on small groups of people and those thought to have been exposed to abnormally high levels of radiation.
The ABC reports radioactive iodine tends to accumulate in children's thyroid glands more than those of adults, placing them at greater risks of diseases such as cancer.
