Illness as Metaphor is a nonfiction work written by Susan Sontag and published in 1978. She wrote it during her own fight against breast cancer and challenged the "blame the victim" mentality behind the language society often uses to describe diseases and those who suffer from them.

Drawing out the similarities between public perspectives on cancer (the paradigmatic disease of the twentieth century), and tuberculosis (the symbolic illness of the nineteenth century), Sontag shows how both diseases have become associated with personal psychological traits. In particular she demonstrates how the metaphors and terms used to describe both syndromes lead to an association between repressed passion and the physical disease itself. She notes the peculiar reversal that "With the modern diseases (once TB, now cancer), the romantic idea that the disease expresses the character is invariably extended to assert that the character causes the disease – because it has not expressed itself. Passion moves inward, striking and blighting the deepest cellular recesses."

This subject is expanded upon in Sontag's 1988 work, AIDS and Its Metaphors.