ABSTRACT The first genuine psychobiography, Sigmund Freud's Leonardo da Vinci and a Memory of His Childhood (1910/1957b), presented several important guidelines for psychobiographical research Among them were the rejection both of pathography and of idealization, and the avoidance both of arguments built upon a single clue and of strong conclusions based upon inadequate data Though the guidelines are sound, Freud violated those guidelines in the very work where they first appeared Freud's methodological errors and his “obsession” with the Leonardo book are traced in part to his projective identification with Leonardo, incorporating aspects of his own sexual history and his anxieties about the future of the psychoanalytic movement