In 2020 in the Netherlands, approximately 700 adult patients were diagnosed with differentiated thyroid carcinoma (DTC). Patients with DTC are treated according to the DTC guideline, and in this thesis we investigated different gaps in the current DTC guideline. In general, the treatment of DTC consists of surgery followed by radioactive iodine therapy. Before the treatment with radioactive iodine therapy, patients have to follow a low iodine diet. In this thesis we showed that a low iodine diet of four days is sufficient to prepare patients for this treatment. After treatment, patients will be followed to detect possible recurrent disease. During this follow-up, thyroid protein thyroglobulin (Tg) is determined in the blood because it helps with detecting possible disease. However, 25% of the DTC patients have antibodies against Tg which could make the Tg result unreliable. In this thesis we provide guidance how to interpret Tg in the presence of these antibodies so Tg can still be used during the follow-up of these DTC patients. Paediatric DTC is a rare disease with an excellent prognosis and survival rate. For this reason it is important to investigate the long-term effects and the optimal treatment for this disease. The long-term effects investigated in this thesis were the bone mineral density (BMD) and psychosocial development of adults treated for paediatric DTC. Fortunately, most paediatric DTC survivors showed a normal BMD and psychosocial development. In addition, we developed national recommendations for the treatment of paediatric DTC, and a summary of these recommendations were described in this thesis.