Hypothyroidism remains a common late effect after irradiation of the neck/mediastinum for Hodgkins lymphoma (HL). We evaluated the protective effect of TSH suppression during neck/mediastinum irradiation. From 1998 to 2001, 14 consecutive euthyroid children were given, before and until the end of their radiotherapy on neck/mediastinum, L-thyroxine at TSH-suppressive doses. The 14 patients had adequate TSH suppression during irradiation in 8, inadequate in 6. The 8-year hypothyroidism-free-survival after irradiation was 75 ± 15% for the former group, 0% for the latter (P = 0.009). TSH suppression could have a protective effect on thyroid function as shown in a small group of patients with HL. Pediatr Blood Cancer 2011;57:166–168. © 2011 Wiley-Liss, Inc.