During the study period, 11,708 patients with thyroid cancer were enrolled. The mean follow-up period was 6.08 years (SD 3.82) for the I-131 cohort and 6.87 years (SD 3.95) for the non-I-131 cohort. The demographic data and comorbidities of the I-131 and non-I-131 cohorts are presented in Table 1. The majority of the study participants were in the age range of 15 to 39 years. Patients in the I-131 cohort were more likely to have had a prior abortion (8.87% vs 6.86%, P