Oportunidades was an innovative anti-poverty program that put additional resources in the hands of women and their families and encouraged parents to invest in the human capital of their children. This program was the first in its kind, and early evaluations demonstrating its success informed its large expansion within Mexico and the implementation of similar conditional cash transfer programs across the world. However, the existing evidence, which arguably captures causal positive impacts, relies on a sample of very poor rural children. This paper conducts the first evaluation of the program using representative data. It focuses on child height as a marker of long-term nutritional status. The causal impact of the program on child height is isolated by exploiting insights from the biology of child growth in combination with the timing of the rollout of Oportunidades and the panel dimension of the survey. Height for age among children exposed during the first four years of life is contrasted with similar children who were not exposed. Consistent with previous evidence, this analysis finds positive and sizable effects on children who lived in rural poor communities incorporated at the beginning of the intervention. In contrast, the impacts of the program in rural localities incorporated later and in suburban and urban communities are, at best, very modest.