 Baldorioty de Castro was born in Guaynabo to a poor family. His family moved to San Juan when he was young, where he received his primary education as a student of the noted educator, Rafael Cordero. After completing his elementary education, he enrolled in El Seminario Conciliar de Idelfonso, which at that time was the most organized institution in Puerto Rico. He spent most of his adolescent years studying, and finished with one of the best averages in his class.
