To evaluate serum thyroglobulin (Tg) level as a marker of the development of thyroid disease when following individuals who received neck irradiation therapy in childhood. In a non-randomized cross-sectional study Tg was assessed in 172 survivors of childhood cancer 10.8 y (1.9-24) median (range) after diagnosis and 7.9 y (0.9-24.3) median (range) after the end of treatment. The patients were divided into two groups: group 1 included 47 patients who had received irradiation to the neck and group 2 included 125 patients who did not receive irradiation to the neck. Patients who had received irradiation to the neck had significantly higher Tg levels compared with those who did not receive neck irradiation: median 14.0 (1.0-189.0) microg/L vs median 8.8, (0.7-112.2) microg/L (p < 0.001). Six out of seven patients with elevated Tg levels (>70 microg/L) had received neck irradiation. Among these six patients, two patients developed secondary differentiated thyroid cancer and two patients developed benign thyroid neoplasms. None of the patients who had normal levels of Tg developed thyroid cancer. A high Tg level should be a cause for further investigation in the follow-up of individuals who have received irradiation therapy in childhood.