Objective Alcohol use disorder (AUD) is a global burden but is also one of the most undertreated mental disorders. This study estimates the treatment rate (i.e., help-seeking status) of high-risk drinkers and factors associated with not receiving treatment in Korea using nationally representative National Health Insurance Service-National Sample Cohort (NHIS-NSC) data. Methods Among 1,025,340 participants, we eliminated those under 20 and those who did not respond to the question regarding alcohol consumption. High-risk drinkers were classified based on their frequency and quantity of alcohol consumption (4 or more drinks for women, 5 or more drinks for men per day on average). In total, 32,225 high-risk drinkers were checked for an actual AUD diagnosis to see their treatment-seeking status. Results Among 32,225 high-risk drinkers, only 1.24% had an AUD diagnosis, showing that over 98% of those who could be diagnosed with AUD are not seeking treatment. Factors associated with not seeking treatment were female sex, BMI higher or equal to 18.6, former smoker, middle-aged, and Charlson Comorbidity Index (CCI). Conclusion Our data show that many high-risk drinkers do not seek treatment in Korea. Experts, policymakers, and clinicians should promote help-seeking behavior for AUD and pay close attention to those at risk of not receiving treatment for AUD.