Abstract: Between 1996 and 2008 annual donor expenditure on HIV/AIDS increased from US$300 million to US$7.7 billion. However, HIV incidence has fallen only slightly and there is little evidence of a HIV prevention intervention succeeding at scale. This paper estimates the effect of prevention of mother-to-child transmission (PMTCT) expansion on child mortality in Zambia. My results suggest that the local introduction of PMTCT reduced infant mortality rates by approximately 2 percentage points, or roughly 20 percent. This appears to be the first causal evidence of a HIV prevention intervention succeeding at scale in Sub-Saharan Africa.