It is well-known that socioeconomic status is associated with mental illness at both the individual and population levels, but there is a less clear understanding of whether socioeconomic development is related to poor mental health at the country level.

We aimed to investigate sociodemographic disparities in burden of mental disorders, substance use disorders and self-harm by age group.

Estimates of age-specific disability-adjusted life years (DALY) rates for mental disorders, substance use disorders and self-harm from 1990 to 2019 for 204 countries were obtained. The sociodemographic index (SDI) was used to assess sociodemographic development. Associations between burden of mental health and sociodemographic development in 1990 and 2019 were investigated, and sociodemographic inequalities in burden of mental health from 1990 to 2019 by age were estimated using the concentration index.

Differential trends in sociodemographic disparities in diseases across age groups were observed. For mental disorders, particularly depressive disorder and substance use disorders, DALY rates in high SDI countries were higher and increased more than those in countries with other SDI levels among individuals aged 10–24 and 25–49 years. By contrast, DALY rates for those over 50 years were lower in high SDI countries than in countries with other SDI levels between 1990 and 2019. A higher DALY rate among younger individuals accompanied a higher SDI at the country level. However, increased sociodemographic development was associated with decreased disease burden for adults aged ≥70 years.

Strategies for improving mental health and strengthening mental health system should consider a broader sociocultural context.