This article brings new evidence and a revisionary argument to the debate over Mexico's exceptional relations with Cuba in the decade after the Cuban Revolution. It uses recently declassified Mexican intelligence records to show that Mexican leaders defended Castro primarily because they were afraid of domestic leftist groups and individuals. The first part of the article examines the intelligence information that Mexican decision makers received about internal threats, drawing out the connections that they perceived between Cuba and the Mexican left and the reasons they designed their foreign policy for domestic ends. The second section shifts to the international level, challenging the traditional arguments that foreign or ideological factors determined Mexico's policy toward Cuba. It examines the ways that Mexican leaders defused and negotiated against possible repercussions from Cuba or the United States as a result of their decision to maintain relations with Castro's government. Este articulo ofrece nuevas evidencias y un argumento revisionista al debate sobre las relaciones excepcionales entre Mexico y Cuba durante la decada siguiente a la revolucion cubana. Con base en documentos recien desclasificados de los servicios mexicanos de inteligencia, el articulo muestra que los lideres mexicanos defendieron a Castro fundamentalmente porque tenian miedo de los grupos y activistas de la izquierda local. La primera parte del articulo examina la informacion que los lideres mexicanos recibieron sobre amenazas internas y las razones por las cuales disenaron su politica exterior con fines domesticos. La segunda parte cuestiona el argumento tradicional de que ciertos factores externos o ideologicos determinaron la politica mexicana hacia Cuba, y tambien examina como los lideres mexicanos se prepararon contra las posibles repercusiones desde Cuba o los Estados Unidos que podian haber resultado de la decision mexicana de mantener relaciones con el gobierno de Castro.