Background: This study aimed to measure fear of thyroid cancer in the general U.S. population and identify factors associated with a high level of thyroid cancer-specific fear that may contribute to overtreatment. Methods: We conducted a cross-sectional survey using Prolific Academic Ltd.®, an online survey platform. The survey was administered in August 2020 to English speaking adults (>17 years) in the United States who were registered with Prolific. The target sample was stratified to represent the demographics of the U.S. population. A validated, eight-item breast cancer fear scale was adapted to measure thyroid cancer-specific fear. Multivariate logistic regression identified factors significantly associated with high levels of thyroid cancer-specific fear. Results: Of the 1136 respondents (94.3% eligibility), 50.4% were female, 74.1% White, and the mean age was 45 years (SD = 16 years). Overall, 47.5% of respondents had high levels of thyroid cancer-specific fear. Multivariate regression demonstrated that age <40 years (OR = 2.46 vs. 65+ [95% confidence interval {CI} = 1.60-3.80]) and female gender (OR = 1.48 vs. male [CI = 1.13-1.93]) were associated with high levels of thyroid cancer fear. Believing thyroid cancer (OR = 2.71 [CI = 1.99-3.69]) and cancer in general are serious (OR = 1.53 [CI = 1.13-2.08]) were also associated with high levels of thyroid cancer fear. Respondents who overestimated thyroid cancer incidence (OR = 1.64 [CI = 1.25-2.13]) and believed they had a high chance of developing cancer (OR = 1.70 [CI = 1.19-2.42]) were also more likely to have high fear of thyroid cancer. Conclusion: Thyroid cancer-specific fear is prevalent in U.S. adults particularly in females and those younger than 40 years. Because disease-specific fear is associated with overtreatment, targeted education about the seriousness, incidence, and risk factors for developing thyroid cancer may decrease public fear and possibly overtreatment related to "scared decision-making."