Thyroid ultrasound and fine-needle aspiration (FNA) have been implicated in the overdiagnosis of thyroid cancer. To study how the use of diagnostic tools impacts thyroid cancer incidence, we propose using physician age as a surrogate. We aimed to determine whether thyroid cancer incidence is higher in areas with a high density of young physicians compared with areas with a high density of older physicians. SEER 13 database was used to determine thyroid cancer incidence. These data were linked to the Area Resource File data (2000), containing information on physician age at a county-specific level. Cohorts were divided by age based on the concentration of physicians within a population of 1,000,000 persons. The study period was divided into two time periods (1992–1995, 2006–2009). The incidence of thyroid cancer was stable in areas with high concentrations of young and older physicians during the 1992–1995 time period [<35: 5.97; 55–64: 6.82; ≥65: 6.70 (per 100,000py)]. Areas with high concentrations of young physicians had an increased incidence of thyroid cancer compared with areas of high concentrations of older physicians during the 2006–2009 period [<35: 13.3; 55–64: 9.86; ≥65: 7.47 (per 100,000py)]. Thyroid cancer incidence was lower in areas with high concentrations of older physicians. This may be the result of increased adoption of thyroid ultrasound and FNA among younger physicians who have trained after diagnostic tools became common. Age of the diagnosing physician is a surrogate for diagnostic utility contributing to thyroid cancer trends.