Thyroid Ultrasound in Korea: Why the Answer Here Is Often "Watch," Not "Operate"

I keep seeing the same worry from Americans online — especially from Korean Americans, who follow Korean medicine closely — posted right through the first half of this year: Korea over-diagnoses thyroid cancer, and Korean doctors operate too readily. They are describing a Korea that existed a decade ago.

Two things are true here now. A physician performs your thyroid ultrasound personally, and Korean guidelines push toward watching a small cancer rather than removing it. The person judging your nodule is the one holding the probe, and finding something does not automatically start a surgical conversation. 

Korea learned this the hard way

From the late 1990s, thyroid ultrasound spread through Korean health checkups — cheap, quick, easy to add on. Diagnoses exploded and Korea's incidence became the highest in the world. Then came the part that mattered: the death rate did not move. Incidence soaring while mortality stays flat is the signature of overdiagnosis. The scans were finding real cancers that were never going to hurt anyone.

The New England Journal of Medicine published it in 2014 as "Korea's Thyroid-Cancer 'Epidemic' — Screening and Overdiagnosis," and practice shifted fast: thyroid surgery volume fell by about a third in a single year. So the worry Americans carry is a real memory. It is just an old one.

What the correction built

It did not stop at doing less. It became written rules.

The Korean Society of Thyroid Radiology publishes its own ultrasound risk-stratification system, K-TIRADS, revised in 2021 to reduce "unnecessary biopsies for benign nodules while maintaining an appropriate sensitivity for the detection of malignant tumors." It raised the size at which a nodule gets biopsied, and a nodule graded benign is not biopsied at all.

In 2025 the Korean Thyroid Association issued a guideline stating that adults with low-risk papillary microcarcinoma "may be considered for AS" — active surveillance. Watched, not operated on.

One system for deciding when not to biopsy, a second for when not to operate.

With 15 Samsung Medison R20 flagship ultrasound systems, Bumin Prestige has virtually no wait time. (Source: Bumin Prestiage)

Why a doctor holds the probe

Ultrasound is not like CT or MRI. There is no complete dataset to review afterward: the exam happens live, and whoever moves the probe decides what gets seen and how it is measured. In Korea that has to be a physician — the Supreme Court confirmed in 2022 that a technologist scanning independently is unlicensed practice.

So the judgment about your nodule is made by a doctor, at the moment of the exam, in a country that performs an enormous number of these studies. That is a reading problem, not a scanning problem.

What this means for you

Nodules are common and the overwhelming majority are benign. What decides your next step is not that a nodule exists but its size and its features on ultrasound.

One thing catches Americans off guard: bring your report from home, and expect to be scanned again anyway. Nobody can re-read someone else's live exam, so a new scan is not an upsell — it is how the test works. Prior measurements still help, because change over time is one of the things a doctor weighs. But the decision comes from the exam and workup done here, and no one should shortcut a diagnosis on the strength of paperwork from abroad.

If you have no nodule and no symptoms, whether to add the scan is a conversation to have with a doctor rather than a box to tick on a menu. We are not clinicians and we will not tell you to take a test or to skip one. What we can tell you is what physicians weigh: family history, a palpable lump, an abnormal TSH, prior radiation to the neck. Bring those to the discussion — and it is worth knowing the history, because adding this scan simply for being cheap and available is how Korea got here.

We wrote separately about what early detection does and does not buy you, and Himedi can help you choose the package that fits your reasons. Your health, your journey.

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About the Author

Donkyo Seo
Co-founder & CEO, Himedi

For the past 9 years, Donkyo has helped international patients navigate Korean healthcare. Himedi is licensed by Korea's Ministry of Health & Welfare (License #A-2016-01-01-2345). 

Sources

• Korean Society of Thyroid Radiology. "2021 Korean Thyroid Imaging Reporting and Data System (2021 K-TIRADS) and Imaging-Based Management of Thyroid Nodules: Consensus Statement and Recommendations." Korean Journal of Radiology 2021. doi:10.3348/kjr.2021.0713
• Korean Thyroid Association. "2025 Korean Thyroid Association Clinical Management Guideline on Active Surveillance for Low-Risk Papillary Thyroid Carcinoma." Endocrinology and Metabolism, June 24, 2025
• Supreme Court of Korea, en banc decision 2016Do21314, December 22, 2022 — independent performance of ultrasound examination by a radiologic technologist constitutes unlicensed medical practice
• Ahn HS, Kim HJ, Welch HG. "Korea's Thyroid-Cancer 'Epidemic' — Screening and Overdiagnosis." New England Journal of Medicine 2014;371:1765–1767. doi:10.1056/NEJMp1409841
• Ahn HS, Welch HG. "South Korea's Thyroid-Cancer 'Epidemic' — Turning the Tide." New England Journal of Medicine 2015;373:2389–2390. doi:10.1056/NEJMc1507622