On My Life is the autobiography of the famous Milanese physician, Girolamo Cardano (1501–1576/77). It was posthumously published in Paris in 1643 by the editorship of the French scholar Gabriel Naudé (1600–1653). This piece of work, extremely complex and difficult to understand for modern readers, is richly illustrated by elements based on Cardano’s personal dream interpretations, and its structure borrows models from Greek astrology and medicine. It is also colored by his lifelong experience of phenomena related to his “guardian spirit,” which finally appeared in the guise of his father, Fazio. This paper tries to decipher these elements by using his other writings, namely the Commentary on Ptolemy’s Tetrabiblos (1554), On My Own Books (1557 and 1562), Books on Synesian Dreams (1562) and Dialogue between Girolamo and his Father Fazio (written ca. 1574).