This paper analyses the way Italian paintings and artistic theory from the late Renaissance conceptualised ugliness, and gradually drew it closer to beauty. The first part of this article focuses on the traditional notion of ugliness as the mere opposite of beauty, in other words, ugliness as an expression of formal disharmony. The second part deals with the evolution from this conceptual antithesis to the paradoxical entwinement of these two notions, which led some authors to endow ugliness with qualities which had hitherto been applied to beauty. We consider several forms of ‘beautiful ugliness’: those of the “cruel and horrible” (Gabriele Paleotti) sacred paintings whose beauty resides in their faithful rendering of the Scriptures, or, in other words, in their truthfulness; those of the Silenus-like characters whose kindness pierces through revolting physical traits; those of the artistic ‘capricci’ who, under their apparent deformity, hide the ingenuity of their creator; and those who take up the Aristotelian paradox, according to which the correct imitation of ugliness arouses a feeling of pleasure among the spectator. In the Baroque aesthetic (third part), the ‘beautiful ugliness’ is an oxymoronic creation in which the horrifying content of the mimesis is consciously used in order to highlight, by contrast, the transformative power of the artist. The conceptualisation of caricature in the 17th century, which we mention in the fourth part of this work, suggests that beauty and ugliness, at least in their ideal forms, are in fact the two sides of a same coin.