Background: The 2015 American Thyroid Association (ATA) guidelines recommended that low-risk, differentiated thyroid cancers (DTC) between 1 and 4 cm may be treated with thyroid lobectomy alone. We sought to determine the effect of these guideline changes on the rate of completion thyroidectomy (CT) for low-risk DTC and factors influencing surgical decision-making. Methods: All patients from 2014 to 2018 who received an initial thyroid lobectomy at our institution with final pathology demonstrating DTC were included. Patients were divided into “pre” and “post” guideline cohorts (2014–2015 and 2016–2018, respectively). The rate of CT was compared between the two cohorts. Patient demographics and tumor characteristics were examined for association with CT. Results: A total of 163 patients met study criteria: 63 patients in the 2014–2015 (“pre”) and 100 in the 2016–2018 (“post”) group. In the “pre” period, 41 (65.1%) patients received CT compared with 43 (43.0%) in the “post” period (p < 0.01)—a 34% decrease in the rate of completion surgery (p < 0.01). Of low-risk patients with DTC between 1 and 4 cm in size, 17 of 35 (48.6%) received CT in the “pre” period compared with 15 of 60 (25.0%) in the post period—a 48.6% decrease in the rate of completion surgery (p = 0.02). Greater tumor size, capsular invasion, and multifocality were associated with CT in low-risk “post” guideline patients (p < 0.05 for all). Conclusions: The rate of CT decreased significantly by 48.6% for low-risk patients with DTC between 1 and 4 cm, demonstrating recognition of the 2015 ATA guidelines. However, 25% of these patients underwent CT, suggesting additional factors influencing the decision for further treatment.