Since the late 1990s, the epidemic of human immunodeficiency virus (HIV) infection in Taiwan has expanded dramatically. Pediatric HIV infection has also increased at an alarming pace. Nearly 40% of the HIV-infected children (<10 years) contracted infection through mother-to-child transmission (MTCT). The aims of this study were to evaluate the effects of interventions to prevent MTCT of HIV infection, and to describe the clinical and immunologic characteristics of children born to HIV-seropositive mothers in southern Taiwan. From 1995 to 2003, an observational, longitudinal study of 8 children born to HIV-infected mothers was carried out at a tertiary care university hospital. The median age at enrollment was 0.4 years (range, 1 day-7.5 years), and the mean duration of follow-up was 2.7 years. Four mothers were immigrants from southeastern Asia. Due to antenatal diagnosis of maternal HIV infection, 3 children underwent interventions, including cesarean section, prophylactic use of zidovudine, and bottle-feeding in order to prevent vertical transmission. Five children were born without interventions because of delayed diagnosis of maternal HIV infection. During follow-up, 2 children were found to be HIV-infected and 6 were not infected. The rate of MTCT was lower among patients with interventions (0% vs 40%). In HIV-exposed/non-infected children, the clinical and immunologic assessments were normal during follow-up. Both HIV-infected children progressed to the stage of acquired immunodeficiency syndrome. Early identification of HIV-seropositive pregnant women, implementations to reduce vertical transmission, and introduction of antiretroviral therapy permit optimism in the prevention and treatment of pediatric HIV infection.