Trends in the US and Australian suicide mortality have shifted over the last 100 years, with notable differences between age groups and genders.

This study compared overall and gender- and age-specific suicide rates from 1921 to 2020 in the USA and Australia to determine long-term variation for each country.

Suicide data (1921–2020, inclusive) were obtained from the US Centers for Disease Control and Prevention and the Australian Institute of Health and Welfare. Poisson regression was used to assess whether suicide rates between groups were significantly different.

Overall suicide rates were higher in the USA compared to Australia, from 1921 to the 1940s, but were similar from the 1950s onwards. While male suicide rates fluctuated, female suicide rates were relatively stable (except for Australian women in the 1960s). In the USA and Australia, suicide rates for young males have significantly increased since the 1950s, while they have decreased for the older male population since the 1940s.

While overall national suicide rates were relatively stable over 100 years apart from during war and economic depression, male suicide rates in the USA and Australia experienced significant age-related changes over the century. These include major declines in males aged over 65 years but also an increase in suicides for those aged between 15 and 44. Suicide rates across age groups have therefore converged, regressing towards the mean for all age groups combined.