Background: Active surveillance (AS) has been established as an alternative to immediate surgery for low-risk papillary thyroid microcarcinoma (PTMC). Nonetheless, it remains difficult to decide between AS and immediate surgery, since limited objective evidence exists regarding risks and benefits. The aim of study is to compare the cumulative costs of AS and immediate surgery. Methods: To estimate cumulative costs, a hypothetical model is simulated based on the Multicenter Prospective Cohort Study of Active Surveillance on Papillary Thyroid Micro-Carcinoma (MAeSTro) study, a multicenter prospective cohort study of AS for PTMC. Direct and indirect costs are estimated from diagnosis to the treatment decision and follow-up for 10 years and a longer period. In the case of the scenarios, AS, AS to surgery due to changing their mind, and lobectomy (analyzed regardless of levothyroxine [LT4] treatment, as well as subdivided into lobectomy/LT4[-] and lobectomy/LT4[+]) are considered. A sensitivity analysis is performed using different discount rates to address uncertainties in future time costs. To compare the cumulative costs, we referred to previous research conducted in Hong Kong, the United States, and Japan. Results: The initial cost of AS is estimated to be 5.6 times lower than that of lobectomy (regardless of LT4 use), while the 10-year cumulative costs of AS ($2545) and lobectomy regardless of LT4 ($3045) are similar under a discount rate of 3%. However, in the long-term follow-up period, immediate surgery is going to be estimated more economical than AS. The costs of the two management approaches are similar in Hong Kong, but substantially different in the United States and Japan, implying that it could be affected by each country's national health insurance coverage and the thyroid ultrasound interval during follow-up. Conclusion: Considering both direct and indirect costs, the cumulative costs of AS and immediate surgery in low-risk PTMC patients are similar during 10 years, and surgery could be more economical for patients with a life expectancy in long-term follow-up. However, careful interpretation is needed for long-term follow-up and the country's health care system and environment. Nevertheless, considering the representative protocols and objective costs in South Korea, it is expected to be a key to suggest the appropriate treatment for PTMC patients.