Since the mortality rate for childhood differentiated thyroid carcinoma is nearly zero, the focus must be to minimise morbidity following treatment. Our aim was to analyse early and late adverse events. Twenty-five of 26 children treated between 1962 and 2002 were evaluated. Median follow-up was 14.2 years (range 0.9-39.4 years). All underwent total thyroidectomy, 15 (60%) with lymph node dissection and 15 (60%) with adjuvant radio-iodide therapy. Mortality was zero. Seven developed recurrent disease, two developed a third recurrence. Twenty-one (84%) had > or =1 adverse event. Eight had permanent hypoparathyroidism (PH), six permanent recurrent nerve paralysis (PRNP) and two Horner's syndrome. Risk factors for PH and PRNP were total thyroidectomy with lymph node dissection (RR: 6.45, P = 0.015) and recurrent nerve tumour encasement (RR: 8.00, P = 0.001), respectively. Other adverse events were fatigue (n = 5), scar problems (n = 4) and chronic myeloid leukaemia (n = 1). These results emphasise the need to improve treatment strategies.