• A mathematical model was developed to assess the effect of various assumed prevalence rates of maternal human immunodeficiency virus (HIV) infection on perinatally acquired HIV infections and child survival. The model indicates that for children younger than 5 years, countries with low baseline mortality rates will experience greater relative increases in child mortality rates and larger proportions of HIV-caused deaths in children than countries with high mortality rates. It also suggests that perinatal HIV infection could become the most common cause of deaths in children in the developed world if maternal infection rates reach 2% to 3%. Rates of 25% to 30% would be needed to produce a similar effect in the developing world. Child survival gains in the last three decades in the developed world could be quickly erased at low levels of maternal HIV infection, but gains would not be completely offset in the developing world until more than 40% of mothers became infected with HIV. When basic demographic information and the maternal HIV infection rate are known, the model permits a direct assessment of infant and child mortality caused by HIV. It can also be used to estimate the prevalence of maternal HIV infection when values for all other variables are known.