Background Uruguay, a South American country of 3.4 million inhabitants that has already banned tobacco advertising, prohibited such terms as light, mild and low-tar and required graphic warnings covering 80% of cigarette packs, is considering the imposition of plain, standardised packaging.

Methods We conducted an experimental choice-based conjoint analysis of the impact of alternative cigarette package designs on the risk perceptions of 180 adult current Uruguayan smokers. We compared plain packaging, with a standardised brand description and the dark brown background colour required on Australian cigarette packages, to two controls: the current package design with distinctive brand elements and colours; and a modified package design, with distinctive brand elements and the dark brown background colour. Graphic warnings were also varied.

Results Plain packaging significantly reduced the probability of perceiving the stimulus cigarettes as less harmful in comparison to the current package design (OR 0.398, 95% CI 0.333 to 0.476, p<0.001) and the modified package design (OR 0.729, 95% CI 0.626 to 0.849, p<0.001).

Conclusions Plain packaging enhanced the perceived risk of cigarette products even in a highly regulated setting such as Uruguay. Both the elimination of distinctive brand elements and the use of Australia’s dark brown background colour contributed to the observed effect.