Oportunidades, Mexico's most important antipoverty program, currently with 5 million enrolled households in all regions of the country, has been shown to significantly contribute to improving the nutrition, health, and education of the poor. Because the program has used different enrollment strategies in rural and urban areas and has both obligatory (e.g., health and nutrition education) and nonobligatory components (e.g., nutrition supplements for children younger than 2 y of age), it provides an excellent opportunity to study program enrollment and utilization of different program components. In urban areas enrollment was more complex, and hence enrollment was much lower then in rural areas where the process was quasiautomatic, and nearly all eligible households enrolled. Enrollment in urban areas was not associated with having a child younger than 2 y of age. Utilization was notably higher with the obligatory than with the nonobligatory program components, illustrated by the inadequate consumption of the nutrition program's supplement as compared with near-universal compliance with well-baby visits. Innovative approaches, some of which are currently being tested, are needed to further increase the program's impact.