This article explores the significance of sculptural and painted representations of ‘overweight’ and ‘underweight’ body types in the visual culture of Roman Italy from the fourth century bc through to the late Empire, and considers the relationship of this imagery to Greek and Hellenistic precedents. In spite of the topical character of fat in 21st-century sociology, anthropology and medical science, obesity and emaciation in the ancient world remain almost completely unexplored. This article sets out to examine the relationship of fat and thin bodies to power, wealth, character and behaviour, and seeks to identify patterns and continuities in the iconography of fleshiness and slenderness across a stretch of several hundred years. Such bodies could be evaluated in a number of different ways, and this article exposes the diverse — and sometimes contradictory — responses to body fat in the art and culture of the Roman world. It first examines the significance of obesity and emaciation in language, literature and medicine, and then discusses visual representations under three headings: ‘Fertility’; ‘The marginal and the ridiculous’, examining the relationship between body fat, humour and figures at the edge of civilized society; and ‘Portraits’, exploring fat and thin in the portraiture of real-life individuals in the realms of philosophy, Hellenistic rulership, Etruscan funerary art and Roman public sculpture.