The Aldine edition of Galen, awaited for more than 25 years, was perhaps the most risky enterprise in the whole history of the publishing house, and it almost brought Aldus' heirs to bankruptcy. Although the editors were among the most renowned specialists of the time, the edition was harshly criticized by one former friend and collaborator of Aldus, Desiderius Erasmus of Rotterdam. Why? Was the edition so bad, were the manuscripts on which the edition was based responsible for its quality? Or were there other reasons for Erasmus' complaint? This paper tries to give some hints in order to answer such questions, arguing that the role of Erasmus in the assessment of the value of the edition should take us into Aldus' house in the period of the late fifteenth and early sixteenth century, and into the political and religious debate of the time.