Objective: The aims were to analyse the features of papillary thyroid carcinoma in a large cohort of children and adolescents in Belarus and to study the influence of radiation exposure as well as the source of irradiation on the morphological and clinical presentations of tumours.

Design and patients: The clinical and pathological features of 1086 young patients (age range = 4 to 18 inclusive, followed up for ≥ 18 years) with papillary thyroid carcinoma diagnosed during the years 1990 to 2010 were reviewed. The patients were divided into three groups: “external radiation-related”, “post-Chernobyl” (internal irradiation-related) and “sporadic”. Besides, patients from “post-Chernobyl” cohort (n = 936) were further divided into the three equal subgroups according to the dates of surgery, which were corresponding to the early (4–9 years), intermediate (10–12 years) and long (14–18 years) latency periods.

Results: Patients in the “external radiation-related” group often showed extra-thyroidal extension in tumours sized ≤ 10 mm (p = 0.002). Distant metastases were more frequently (p = 0.006) discovered in patients with papillary thyroid carcinoma in post-Chernobyl group (104 of 936, 11.1%) when compared to juveniles from other two groups. Lateral nodal disease and distant metastases were often noted in post-Chernobyl patients operated during the early and intermediate latency periods only.

Conclusion: Young patients in Belarus with papillary thyroid carcinoma in the “post-Chernobyl” group differed in many clinical and pathological parameters from those in the “sporadic” group. “External radiation related” papillary thyroid carcinomas were distinguished from other two groups of carcinoma in more advanced local spread and more aggressive behaviour of micro-carcinomas.