Background: The number of people completing suicide in Australia increased steadily between 1980 and the mid-1990s, and then subsequently declined sharply.In contrast, the number of people attempting suicide has continued to rise over this period.These divergent trends imply a declining case fatality rate, but no previous research has investigated this phenomenon.Methods: We obtained data linked at the individual level on suicide attempts (from hospital admission records) and completions (from the national mortality register) in Western Australia from 1980 to 2007.With 2.4 million residents, Western Australia is Australias 4th largest state.The data were linked at the individual level.We calculated case fatality rates [number of completed suicides / (number of attempted suicides + number of completed suicides)] by method and used multivariable logistic regression to examine changes in patterns of suicide completions over time.Specifically, the unit of analysis in the regression analyses was the "suicidal event" (attempt or completion), and the predictors were method used, year, and age and gender of the individual.The model adjusted for clustering of suicidal events among individuals.Results: 78,755 suicidal events led to 5,808 deaths.Case fatality rates declined for all methods, but the largest declines were for motor vehicle exhaust (60% decline) and hanging (36% decline).The regression analyses showed that the odds of dying from an attempt declined for all methods across time, but the effect was not uniform.For instance, for each one-year increase in time, the odds an attempt would cause death declined 2.4% for firearms, 6.5% for hanging, and 7.9% for motor vehicle exhaust and 8.3% for cutting/piercing, controlling for other factors.Extrapolations from the regression model suggest that, had case fatality rates across all methods remained at 1980 levels for the ensuing 27 years, Western Australia would have experienced 48% more suicides.Conclusion: Declining case fatality rates are an important explanation for the decrease in suicides in Western Australia in recent decades and likely also for Australia as a whole.There are three plausible reasons for the decline in case fatality rates.First, some methods (e.g.motor vehicle exhaust) have become less lethal.Second, medical treatments have become timelier and more effective, improving attempters chances of survival.Finally, case fatality rates may have declined due to demographic or behavioural changes among attempters.Further research is needed to disentangle the relative importance of these explanations.Better understanding of what has led to lower case fatality rates could inform and guide future suicide prevention efforts.