Background: Non-European international adoptees in Sweden were shown to have a three-to fourfold higher risk of suicidal behaviour in youth during 1986-1995 compared with the general population. The aim of this study was to investigate whether this high risk persists beyond youth and in later cohorts.

Methods: A register study of Swedish national cohorts born 1972-86 including 20 625 non-European international adoptees, and comparison populations of 10 915 non-European immigrants and 1 435 167 Swedish born was performed. The study population was followed from age 18 between 1991 and 2016, with suicide and hospital admissions due to suicide attempt as outcomes. Poisson regression models of person time in the study, adjusted for gender and household income at age 17, were fitted to calculate relative risks (RR).

Findings: Adjusted RR for suicide in non-European international adoptees was high at age 18-22, 2.74 (95% C. I. 1.95-3.86), but decreased gradually to age 33-43 when the risk was similar to Swedish-born. Adjusted RR for suicide attempts in international adoptees was 2.33 (2.15-2.52) at age 18-22, decreased slightly with older age, but remained higher than Swedish born in all age-classes. Risks for both outcomes were greatest, around three times higher compared with the Swedish-born in the oldest birth cohorts of non-European international adoptees, born 1972-76. Risks for both suicidal outcomes increased with higher age at adoption.

Interpretation: The risk of suicidal behaviour in non-European international adoptees in Sweden decreases with age and is lower in later birth cohorts and in infant adoptions.