['Papillary thyroid carcinoma (PTC) in patients exposed to environmental radioiodine after the Chernobyl accident is thought to have a relatively aggressive clinical course. Long-term results of treatment are not well known, especially in comparison with sporadic PTC.', 'The determination of risk factors for PTC recurrence in a controlled for baseline factors group of patients with radiation-related and sporadic PTC.', 'Retrospective cohort study involving patients treated for PTC and followed-up in 1991-2008. Risk factors were assessed by stratified analysis using the proportional hazard model.', 'Referral center-based.', 'A total of 497 patients were enrolled. Patients exposed to radioiodine were 172 individuals with reconstructed individual radiation thyroid doses ranging 51-3170 mGy. Patients with sporadic PTC included 325 individuals matched to exposed patients for sex, age ± 5 yr and time to treatment ± 2 yr.', 'Cancer recurrence.', 'Nodal disease increased the recurrence rate (HR = 5.21; 95% CI = 1.63-16.7) while the presence of tumor capsule (HR = 0.17; 95% CI = 0.06-0.45) and, particularly, treatment according to the Revised American Thyroid Association Management Guidelines for Patients with Thyroid Nodules and Differentiated Thyroid Cancer significantly reduced it (HR = 0.16; 95% CI = 0.06-0.42). None of the tested variables interacted with radiation factor.'] Does radiation exposure significantly contribute to the risk of recurrence of Chernobyl thyroid cancer?