This is an observational cohort in pediatric HIV patients in China. Children who receive antiretroviral drugs will be recruited in this study. The main objectives are as follows: 1. To establish simpler and smarter pediatric antiretroviral therapy in China including both first-line and second-line regimens. 2. To study the nature, characteristics and mechanisms of immunoreconstitution in HIV-infected children using the data and samples from the pediatric antiretroviral therapy cohort. 3. To establish a basic science and clinical research network based on the pediatric antiretroviral cohort.