Although the number of newly diagnosed cases of HiV is decreasing worldwide, those in Korea have been steadily on the rise, especially among adolescents (ages 10-19 years) and young adults (ages 20-29 years). To identify the characteristics in the new diagnosis among these age groups, we analyzed HIV testing sizes and HIV prevalence under the national HIV surveillance system in Korea in the last six years. We collected data of HIV tests conducted at Blood Banks (BB), Public Health Centers (PHCs), and Military Manpower Administration (MMA) nationwide every year from 2010 to 2015, except for anonymous tests. HIV prevalence, calculated as the number of new HIV-diagnosed cases per 10,000 test-takers per year, was analyzed according to sex, age, institution, and reason for HIV testing. Data were analyzed using logistic regression. In the three testing institutes, there were new cases of HIV with 50% and 75% of cases diagnosed in young adults and adolescents, respectively. The total size of HIV tests at the three sites was approximately 3.5 million tests per year; 80% of these were conducted in BBs, 10% in PHCs, and 10% in MMA. HIV prevalence, according to age, increased across all age groups for the six years, especially prevalent in young adults doubled during that period (1.01 per 10,000 testtakers in 2010, 2.45 in 2015). HIV prevalence among the "suspected" young male adults who visited PHCs for tests, was highest during the six years, increasing 6.5 times in the last two years (315.79 per 10,000 test-takers in 2014, 335.55 in 2015) compared to before 2014. We identified the characteristics of growing HiV infection in Korea as the increase of HiV prevalence among the suspected of young male adults at PHCs. Further, we propose that HIV prevalence in MMA can be used as an essential index for national HIV surveillance of adolescent boys in Korea. HIV infection, known to the public since the early 1980s, has been rapidly spreading worldwide through sexual contact, vertical transmission, blood transfusions, and needle sharing for injection drug use (IDU). The HIV epidemic has different transmission routes and the speed of spreading across countries 1. Globally, for more than 35 years, approximately 78 million individuals have been infected with HIV, with 35 million HIV-related deaths, and 37 million people are currently living with HIV 2. The first HIV-infection in Korea was identified in 1985, and over the next 30 years or so, approximately 15,000 individuals were identified as HIV-infected. It was reported that more than 99% of individuals diagnosed with HIV in Korea were infected via sexual contact, while transmission through blood transfusion, vertical transmission, and needle sharing for IDU was infrequent 3. Soon after the discovery of HIV in Korea, the country initiated a prevention program focused on HIV transmission reduction by regularly performing HIV screening tests on high-risk groups for sexually transmitted infections (STI) and extending it to other groups 4-6. Hospitals or clinics and public health centr...