CONTEXT: Active surveillance (AS) of thyroid cancer with serial ultrasounds is a newer management option in the United States. OBJECTIVE: This work aimed to understand factors associated with the adoption of AS. METHODS: We surveyed endocrinologists and surgeons in the American Medical Association Masterfile. To estimate adoption, respondents recommended treatment for 2 hypothetical cases appropriate for AS. Established models of guideline implementation guided questionnaire development. Outcome measures included adoption of AS (nonadopters vs adopters, who respectively did not recommend or recommended AS at least once; and partial vs full adopters, who respectively recommended AS for one or both cases). RESULTS: The 464 respondents (33.3% response) demographically represented specialties that treat thyroid cancer. Nonadopters (45.7%) were significantly (P < .001) less likely than adopters to practice in academic settings, see more than 25 thyroid cancer patients/year, be aware of AS, use applicable guidelines (P = .04), know how to determine whether a patient is appropriate for AS, have resources to perform AS, or be motivated to use AS. Nonadopters were also significantly more likely to be anxious or have reservations about AS, be concerned about poor outcomes, or believe AS places a psychological burden on patients. Among adopters, partial and full adopters were similar except partial adopters were less likely to discuss AS with patients (P = .03) and more likely to be anxious (P = .04), have reservations (P = .03), and have concerns about the psychological burden (P = .009) of AS. Few respondents (3.2%) believed patients were aware of AS. CONCLUSION: Widespread adoption of AS will require increased patient and physician awareness, interest, and evaluation of outcomes.