Introduction: Australia’s excise and customs duty on tobacco has been automatically increased biannually since 1984. Increases in duty on par with inflation ensured that tobacco stayed at least as costly as other goods. This would be expected to maintain, rather than drive down, smoking prevalence. We examined the association between smoking prevalence and duty over a 10-year period. Methods: Using monthly data from five Australian capital cities, collected from March 2001 to March 2010 among Australians aged at least 18 years, multiple linear regression modeled associations between smoking prevalence and the two components (duty and non-duty) of the recommended retail price of an average packet of cigarettes, adjusting for policy covariates. Results : revalence declined from 23.6% in March 2001 to 17.0% in March 2010 [absolute difference 6.6%; 95% confidence interval (CI) = 6.5% to 6.8%]. Duty increased from $0.2026 to $0.2622 per cigarette over the same period. In the adjusted model, a 1-cent increase in the duty component of price was not associated with changes in prevalence (0.019; 95% CI = -0.035% to 0.028%). Increased non-duty component of price was associated with a decline in prevalence (-0.027; 95% CI = -0.052% to -0.002%). This effect was stronger when changes in income were controlled for. Conclusions: In line with expectations, inflation-adjusted duty was not associated with changes in smoking prevalence, but it may have prevented upward pressure on prevalence that increasing affordability could have exerted. Frequent increases in duty greater than the growth in both wages and goods would more effectively reduce smoking than regular indexation. Implications : ew countries inflation-adjusted excise duty to ensure that tobacco products do not become more affordable; however, Australia experienced a decade of inflation adjustment alone, enabling the impact of this policy to be studied. This study shows that inflation-adjusted duty likely did prevent tobacco becoming more affordable and that indexation was associated with declines in smoking when tobacco companies over-shifted the duty rises (ie, increased price over and above duty rises).The study also suggests that frequent increases in taxation that exceed both wage growth and increases in costliness of other goods are needed to prompt increased rates of quitting.