In this work new data and reflections are brought out to understand better the figure of Lázaro de Soto, doctor of Phillip II, in the Renaissance Spanish Medicine context. Several works of this author remain chiefly as comments on Hippocrates. Lázaro de Soto's care to choose the texts and the richness of his criticism are specially discussed here, along with the accomplished handling of the different authors that constitute the main source of his writings.