BACKGROUND: CD4+ cell counts reflect immunologic status of human immunodeficiency virus (HIV) patients. Recommended CD4+ cell counts for the initiation of highly active antiretroviral therapy (HAART) has increased over the past several years in various HIV treatment guidelines. We investigated the trend of CD4+ cell counts at diagnosis and treatment start using data from the Korea HIV/acquired immune deficiency syndrome (AIDS) Cohort Study. MATERIALS AND METHODS: The Korea HIV/AIDS Cohort Study started in 2006 and enrolled HIV patients from 21 tertiary and secondary hospitals in South Korea. The data for CD4+ cell counts at diagnosis and HAART initiation from these HIV patients were analyzed by three-year time intervals and presented by number of CD4+ cells (≤100, 101-200, 201-350, 351-500 and >500 cells/mm³). The HIV-RNA titer at diagnosis and HAART initiation were presented by 3-year intervals by groups ≤50,000, 50,001-100,000, 100,001-200,000, 200,001-1,000,000, and >1,000,000 copies/mL. RESULTS: Median values of CD4+ cell count and HIV-RNA titer at initial HIV diagnosis were 247 cells/mm³ and 394,955 copies/mL, respectively. At time of initiating HAART, median values of CD4+ cell count and HIV-RNA were 181 cells/mm³ and 83,500 copies/mL, respectively. Patients with low CD4+ cell count (CD4+ cell count ≤200 cells/mm³) at diagnosis (31-51%) and initiation of HAART accounted for the largest proportion (30-65%) over the three-year time intervals. This proportion increased until 2010-2012. CONCLUSION: CD4+ cell count at initiation of HAART was found to be very low, and the increase in late initiation of HAART in recent years is of concern. We think that this increase is primarily due to an increasing proportion of late presenters. We recommend early detection of HIV patients and earlier start of HAART in order to treat and prevent spread of HIV infection.