Following radioiodine (131I) therapy of differentiated thyroid cancer, salivary and lacrimal glands may become inflamed, leading to dysfunctions. The incidence of these dysfunctions after 131I-therapy is poorly known, and no clinical or genetic factors have been identified to date to define patients at risk. The aims of this study are 1) to characterize the dysfunction of salivary and lacrimal glands after 131I-therapy, 2) to identify risk factors of salivary and lacrimal dysfunction. START (Salivary dysfuncTion After Radioiodine Treatment) is a prospective study including 139 patients, candidates for a 131I-therapy in the context of their differentiated thyroid cancer (45 and 94 patients in 1.1GBq and 3.7GBq groups respectively). The follow-up was based on 2 scheduled visits: immediately before 131I-therapy (T0) and 6-months after (T6). At each visit, questionnaires on salivary disorders (validated French tool) and dry eye (OSDI© Questionnaire) were administered, and individual salivary flow measurements (without and with salivary gland stimulation) were performed. Descriptive analyses and paired comparisons tests between T0 and T6 were computed. The T6 follow-up started in March 2021, and is still ongoing. Complete information was provided for 122 patients (71% women, mean age=47.4 (±14.3) y). At 6 months after 131I-therapy, stimulated saliva flow rate decreased (from 6.98 (±3.35) to 6.07 (±3.15) mL/min, p<0.01), as well as the difference between stimulated and unstimulated saliva flow rates (from 1.40 (±0.67) to 1.21 (±0.63) mL/min, p<0.01). Also, after 131I-therapy, 19% and 21% of the study population reported dry eye or dry mouth feeling, respectively. This work presents preliminary results of the START study, showing a decrease in salivary and lacrimal gland activity after 131I-therapy. Further analyses will be performed, including saliva biochemical composition, genetic and epigenetic variants, and dose-response relationships (using dosimetric reconstructions).