Positive body image predicts several measures of happiness, well-being, and sexual functioning. Prior research has suggested a link between communal naked activity and positive body image, but has thus far not clarified either the direction or mechanisms of this relationship. This was the first randomized controlled trial of the effects of nakedness on body image. Two potential explanatory mediators of this effect were also investigated. Fifty-one participants were randomly assigned to one of two groups in which they interacted with other people either naked (naked condition) or clothed (control condition). All participants completed measures of body appreciation before and after the intervention, as well as measures of the relative perceived attractiveness of others and social physique anxiety immediately after the intervention. Perceived attractiveness of others was neither affected by the manipulation nor correlated with body appreciation. However, as expected, participants in the naked condition reported more body appreciation, an effect that was mediated by reductions in social physique anxiety. This research provides initial evidence that naked activity can lead to improvements in body image and evidence of a specific explanatory mechanism. Theoretical and practical implications are discussed.