Background: Given that the introduction of the tobacco plain packaginglegislation in Australia is the first of its kind, research on its real-worldimpact is crucial for policy decision-making in other jurisdictions.Aim: To investigate the impact of Australia’s plain tobacco packaging policyon two stated purposes of the legislation – increasing the impact of healthwarnings and decreasing the promotional appeal of packaging – amongadult smokers.Methods: Serial cross-sectional study with weekly telephone surveys ofadult smokers (April 2006 to May 2013, n = 15,745). Interrupted time-series analyses using ARIMA modelling and logistic regression analyses wereused to investigate intervention effects.Results: Adjusting for background trends, seasonality, and variations inanti-smoking advertising activity and cigarette costliness, results fromARIMA modelling showed that, two to three months after the introductionof the new packs there was a significant increase in the proportion ofsmokers having strong cognitive (B = 0.098, SE = 0.034, p = 0.005), emo-tional (B = 0.086, SE = 0.035, p = 0.01) and avoidant (B = 0.098,SE = 0.028, p = 0.0005) responses to on-pack health warnings. Threemonths following the introduction of the new packs, there was a significantincrease in the proportion of smokers strongly disagreeing that the look oftheir cigarette pack is attractive (B = 0.596, SE = 0.098, p < 0.0001), sayssomething good about them (B = 0.539, SE = 0.089, p < 0.0001), influencesthe brand they buy (B = 0.423, SE = 0.091, p < 0.0001), makes their packstand out (B = 0.546, SE = 0.108, p < 0.0001), is fashionable (B = 0.454,SE = 0.084, p < 0.0001), and matches their style (B = 0.470, SE = 0.086,p < 0.0001). Logistic regression analyses, controlling for demographic andsmoking characteristics, confirmed these effects. Changes in these outcomeswere maintained six months post-intervention.Conclusions: The introductory effects are consistent with the specific objec-tives of the plain packaging legislation. In an environment of strict tobaccopromotion prohibition such as Australia, the plain packaging legislation hasbeen successful in depriving tobacco companies of an ongoing opportunityto promote their products.