Andreas Vesalius rose to unprecedented heights of scientific achievement between the ages of twenty-two and twenty-nine. In the subsequent twenty years he lived an almost sterile life scientifically, and finally died as suddenly as did his career twenty years before. It is the author's assumption that Vesalius—taciturn, melancholic, unpredictable, spirtually sick and morose—suffered from a chronic depressive condition, which must have started between 1543 and 1544. His pathological infantile and adolescent drives, which were the cause of his failure in his personal life, made it possible for him to serve the scientific revolution and humanitarian trends of the Renaissance. This predisposition was, therefore, pathological from the individual, but not from the historical point of view.