Pediatric differentiated thyroid cancer (DTC) is a rare disease. Initial treatment of DTC consists of a (near) total thyroidectomy and radioactive iodine (131I) therapy. Previous studies in adults showed that 131I treatment may result in a reduced salivary gland function. Studies regarding salivary gland function in children treated for DTC are sparse. Our aim was to assess long-term effects of 131I treatment on salivary gland function in survivors of pediatric DTC. Methods: In a nationwide cross-sectional study, salivary gland function of patients treated for pediatric DTC between 1970 and 2013 (>5 years after diagnosis, ≥18 years old at time of evaluation) was studied. Salivary gland function was assessed by sialometry, sialochemistry and a xerostomia inventory. Salivary gland dysfunction was defined as unstimulated whole saliva flow ≤0.2mL/min and/or a stimulated whole saliva flow ≤0.7 mL/min. Results: Sixty-five patients (median age at evaluation 33 [IQR, 25-40] years, 86.2% female, median follow-up period 11 [IQR, 6-22] years) underwent 131I treatment. Median cumulative 131I activity was 5.88 [IQR, 2.92-12.95] GBq, 47.7% underwent multiple 131I administrations. Salivary gland dysfunction was present in 30 (47.6%) patients. Levels of amylase and total protein in saliva were reduced. Moderate to severe xerostomia was present in 22 (35.5%) patients. Stimulated salivary secretion was lower and severity of xerostomia complaints higher in patients treated with higher cumulative 131I activity. Conclusion: In survivors of pediatric DTC, clinically significant salivary gland dysfunction was found in 35.5% and was related to the cumulative 131I activity of the treatment.