This study evaluates the impact of the Mexican conditional cash transfer (CCT) program, Oportunidades and the Nicaraguan program, Red de Protección Social, on vaccination coverage for Bacille Calmette-Guérin (vaccine against tuberculosis), Diphtheria-Pertussis-Tetanus Vaccine, Oral Polio Vaccine and Measles-Containing Vaccine in children less than three years of age, using a randomized treatment and control design at the community level. The intent-to-treat effect on vaccination coverage is assessed using a double-difference estimator. This study found that in Mexico and Nicaragua, CCTs significantly contribute to increased vaccination coverage among children, particularly among those not reached by traditional program strategies, such as children living further from health facilities and with mothers having less than primary school